If a ruling is established in sharee’ah for a reason that no longer applies, and this ruling is in accordance with the fitrah or is one of the symbols of Islam, then it remains even if the reason no longer applies. Raml (walking at a fast pace) in tawaaf was originally intended so that the Prophet (peace and blessings of Allaah be upon him) and his companions could demonstrate physical strength in front of the mushrikeen who said:
There have come to you people who have been weakened by the fever of
This reason no longer applies, but the ruling remains in effect, because the Prophet (peace and blessings of Allaah be upon him) did raml in the Farewell Pilgrimage. So, we do it to follow the Prophet (salallahu alayhi wassalam) who we consider as the best guide.
Apart from that, if you are not going to follow what Prophet (salallahu alayhi wassalam) [whose guidance is the best] did, then people are going to come up with new alternatives to corrupt the religion. Would you consider that as a better thing to follow?
However, in any case, loud or silent, your prayer is valid but it is better if you follow the example of the Prophet.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said:
Reciting out loud in the prayers where this is done is not obligatory,
rather it is what is better. If a person recites silently in a prayer
in which it is prescribed to recite out loud, his prayer is not
invalid, because the Prophet (peace and blessings of Allaah be upon
him) said: “There is no prayer for one who does not recite the Essence
of the Book (al-Faatihah).” He did not specify whether this recitation
is to be out loud or silent. So if a person recites what he is
required to recite, silently or out loud, then he has fulfilled his
duty. But it is better to recite out loud in the prayers where doing
so is customary, as in Fajr and Jumu’ah prayers.
If a person deliberately does not recite out loud when he is leading
the prayer, his prayer is valid but it is lacking.
If a person is praying alone, he has the choice between reciting out
loud or silently. He should look at what is more likely to increase
his focus and humility in prayer, and do that.
Majmoo’ Fataawa Ibn ‘Uthaymeen, 13/73
Source: What is the reason why Qur’aan is recited out loud in some prayers and silently in others?