If Apple made a YouTube-alike or Microsoft, they would likely find the YT creators are champing at the bit to get onto their platform.
Has there ever been a real go at YouTube by a company with significant resources?
Yes I am aware of Nebula but it is not a serious competitor to YouTube. I say that because I tried to use it on PlayStation - which is where I watch all my YouTube and couldn't, which means Nebula is not a serious competitor. Any serious competitor must be available on all the most popular media consumption platforms, and it must not require signup/signin to start watching - that's the baseline set by YouTube.
Even NetFlix - why have they not created a new service for user created content?