Apple is famously compartmentalised & secretive: People working on one product don't even get to go into the building where another product is being developed & the employees working on new products are pretty much forbidden from discussing them outside of their own development team as I understand things.

I would imagine that this makes it very hard for managers of existing products to kill off internal competitors. So long as the board is happy to fund it, you can develop something new without having to play internal big company politics.