Bismillahir Rahmanir Rahim. Alhamdulillahi rabbil-'alamin. Was-Salatu was-Salam 'ala Sayyidina wa Azimina, Wa Habibi Qulubina wa Shafii Nufusina, Abul Qasim Muhammad. Wa 'ala Ahli Bayti tayyibina tahireen.
Why does Allah force us to obey him?
The correct question would be "Why does Allah command us to obey him?". Because Allah does not force anyone. And the answer to this question is given by Allah (azwj) Himself, in Sura Az-Zariyaat (51)
- And I did not create the jinn and mankind except to worship Me.
Quran 51:56
In following Hadith narration, Imam Jafar As-Sadiq is explaining this verse
I asked Abu Abdullah (asws) about the Words of the Mighty and
Majestic: And I have not Created the Jinn and the Humans except to be
worshipping Me [51:56], he (asws) said: ‘Created them for Commanding
them for the worship’.
Source (page 27)
Following verse is evidence that Allah does not force anyone.
There is no compulsion in religion.
Quran 2:256
Furthermore, following verses from Quran 10 are important to be mentioned
99.And if your Lord so Desired, the ones in the earth would believe, all of them in their entirety. So will you force the people until
they become Momineen?
100.And it was not for a soul that it believes except by the Permission of Allah, and He Makes the uncleanness to be upon those who
are not understanding
Quran 10:99-100
And in following Hadith Imam Abu Al-Hassan Ali (asws) Bin Musa Al-Reza (asws) explained these verses to Abbasid Caliph Al-Mamoun
(It has been narrated) regarding questions, which Al-Mamoun asked Abu
Al-Hassan Ali (asws) Bin Musa Al-Reza (asws). So from what he asked,
Mamoun said to him (asws), ‘What is the Meaning of the Words of the
Exalted: And if your Lord so Desired, the ones in the earth would
believe, all of them in their entirety. So will you force the people
until they become Momineen? [10:99] And it was not for a soul that it
believes except by the Permission of Allah [10:100]?’
Al-Reza (asws) said: ‘My (asws) father (asws) Musa Bin Ja’far (asws)
narrated to me (asws), from his (asws) father (asws) Ja’far Bin
Muhammad (asws), from his (asws) father (asws) Muhammad Bin Ali
(asws), from his (asws) father (asws) Ali Bin Al Husayn (asws), from
his (asws) father (asws) Al Husayn Bin Ali (asws), from his (asws)
father (asws) Ali Bin Abu Talib (asws) having said: ‘The Muslims said
to Rasool-Allah (saww), ‘O Rasool-Allah (saww)! If only you (saww)
would force the people by the power against them to be upon Al
Islam, it would increase our number and our strength against our
enemies’.
So Rasool-Allah (saww) said: ‘I (saww) am not going to meet Allah
(azwj) with an innovation in which there would be nothing for me
(saww), and I (saww) am not from the pretenders’.
Thus, Allah (azwj) Blessed and Exalted Revealed: “O Muhammad (saww)!
And if your Lord so Desired, the ones in the earth would believe, all of them in their entirety [10:99] - upon the Way of forcing and
compulsion in the world, just as they are believing when they see the
evil (Punishment) in the Hereafter. And Had I (azwj) done that with
them, they would not be deserving of any Rewards from Me (azwj) not
any Praise, by I (azwj) Want from them to believe out of choice, not
out of compulsion, in order to be deserving from Me (azwj) the
nearness, and the Prestige, and spend an eternity of time in the
eternal Paradise: So will you force the people until they become
Momineen? [10:99].
And as for the Words of the Exalted: And it was not for a soul that
it believes except by the Permission of Allah [10:100]? So that is
not upon the way of a Prohibition against having faith, but it is upon
the Meaning that they were not going to believe until Allah (azwj) had
Permitted it. And His (azwj) Permission is His (azwj) Command for it
for the belief which was responsible and devout, and the forcing it to
the faith at the end of the assignment and the worship from it.
So Al-Mamoun said, ‘You (asws) have relieved me – O Abu Al-Hassan
(asws) – may Allah (azwj) Relieve you (asws)’.
Tafseer Hub-e-Ali(page 57-58)
Why does Allah want to create creatures (humans) and tell them to obey him?
If this is a question of justice then we have better consider following analogy and reason using our A'ql (intellect).
In order to decide whether it is just or not one should compare this case to a case of a businessman who founds a company, to achieve a certain purpose, and hires people to work in this company. Of course the businessman has to pay wage to these people in order for them to work, create for them required conditions, supply with necessary tools and so on. And as these people work, the businessman will benefit from their work, and the people will get wages.
Now let's ask a question here. The owner of the company, is it fair (just) if he demands from these people to obey him? That is, is it fair (just) that he sets rules in this company for these people for them to obey? Trying to answer to this question is trying to answer to the question OP poses.
We do not have to consider the case what happens if the people are not required to obey and the owner of the company does not set rules and regulations as the consequence of it is obvious.
This Dunya (world) is created by Allah and it is His company. The Jinnkind and Mankind are His slaves (workers). This is stated in the following verse
54.Indeed, your Lord is Allāh, who created the heavens and earth in six days and then established Himself above the Throne. He covers the
night with the day, [another night] chasing it rapidly; and [He
created] the sun, the moon, and the stars, subjected by His command.
Unquestionably, His is the creation and the command; blessed is Allāh,
Lord of the worlds.
Quran 7:54
So Allah wants to say
- your Lord is Allāh = I am the businessman;
- who created the heavens and earth = I am the founder of the company;
- established Himself above the Throne = I appoint myself CEO of the company;
- He covers the night with the day, [another night] chasing it rapidly; and [He created] the sun, the moon, and the stars, subjected by His command = I have created all the conditions for my employees;
- His is the creation and the command = My employees have to obey me and I set the rules and regulations in my own company;