So I read this wasn't even originally about Islam, you used to be able to pray to whatever God you had?
>a worship ceremony in Mecca never been about Islam
Yeah. There were hundreds of gods there and pilgrimages were common. You also had to put on the ritualistic garb that they do now when entering Mecca. Not much survived when Islam rose to prominence (Muslims considered it a dark age of ignorance and worked hard to scrub all traces of it that they could), but it is interesting. Poems were there, pictures of Mary and Jesus, various pagan gods, etc.
Muslims believe it was built by Abraham. So, to them that means it must be used as a monotheistic site.
That's probably just an excuse to take control of a pilgrimage site, as well as a trade city.