If leaks are being regularly posted, let's say that an apple feature has been leaked, why don't Android companies implement the feature before apple announces it?

My theory: they want to see if apple succeeds with that feature and if apple does, only then they will copy the feature

Ngl, SailfishOS could have been the third major mobile os but thanks to saturation it couldn't hold it's position. It's such a beautiful operating system that I spent 6 months trying to port it to my device (I failed) but eventually realized that it's not that supported and kind of closed source and dev rarely works on the source. It has it's own advantages and disadvantages but compared to android, it could have been a real deal to iOS