I really didn't find a satisfactory answer to this question.
Isn't the house of god should be open to everyone?
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Simply because, it is a sacred place where God has allowed only Muslims in Makkah, and not pagans. There’s a narration about this. A story begins when the Prophet is about to die, he’s last words was the curse for pagans, and he also expelled all of-’em from Makkah, and now Makkah has become a sanctuary, a Holy place. And because, also prophet Muhammad expelled all of them. That is why. This is already mentioned in Quran.
You can see in here, that God states, ”Oh you who believe! Truly the idolaters are unclean; so let them not, after this year, approach the Sacred Mosque. ..." (9:28). If you’re not satisfied yet, please check in here, even in here it says no none Muslims in Makkah as it is the holiest place in the world, and it is the decision made by God. And also in Islamqa says clearly ”no none Muslims in Makkah.
This only revelation, I didn't find any narration that prohibits the entry of none Muslims in Makkah.