Don't know is the honest answer. However there are "arguments" or "discussions" around why this may have happened.
One of the things that I have seen in my own life is the influence of past culture. So I would argue that Pakistani people still have "beliefs" that are based on their history from the days when it was all India and also the British raaj. A good example is some of the stuff happening during weddings. Islamically a lot of it would be forbidden, or in the case of dowry totally a different/seperate context.
So in Islam a man marries a woman and has to offer a "payment", cash/jewelry or etc. But this is something that is for the woman and he has to fulfil it if he divorces her. Not something the family demand.
Other "reasons" include the lack of education in many parts of the Islamic world. So a reliance on the mullahs etc who are raking it in financially.
I'm some parts the initial "islamacising" was done by sects who were banished from initial muslim lands. So a sort of sectarian version took hold.
Politics. So Islamically a lot of Muslim countries would not be Islamic. I once looked at the constitution of countries who say they are Islamic and they would fail on that basis alone. Pakistan for example is not an Islamic country Islamically and under Islamic jurisprudence a majority Muslim country is not what makes it Islamic. It's ruling system (even if Muslims are the minority) make it Islamic. Even Saudi falls outside with it's constitution.
Influence. So for example as a kid growing up I saw more Muslim men with moustaches than beards. Islam states grow your beard and trim your moustache. But leaders and folk like my dad etc had moustaches in the 70/80s and one theory I read was that in the British army only the officer class could have a moustache and this was in influence.