Common story with platforms, isn't it? It's like a huge magnet drawing everyone to Windows or Intel.
I wonder how much is end user driven, and how much is intermediary driven though. Is it that the customers are only comfortable with one item in each category, or is it the middle men who prefer to sell things that are all connected by the same platform?
Psychology plays a big part, change and differences. Folk don't like change nor difference. You have to be willing to embrace it.
You can do this yourself. Watch your mind freakout and give yourself a panic attack if you were to drag an frequented used app; icon from your phone in to an obscure new location or app folder. Frequent bookmark to another folder or off the bookmark bar.
You get used to it but change is scary because its unknown and so unless you can adjust the user quickly and promptly they will reject whats given to them. Or innovate something whole and new thats never been done before.
Add the fact that major brands have user friendly in hand, trying to convince someone to install Linux with its clunky installer as an example; really throws them off edge.
Nowadays trying to get anyone to change really causes them to melt and its only going to get worse as we go on further through the rabbit hole of social media.
So why change when you already have something that just works, that your used to and friends with. Even if it backstabs you with updates, missing icons and leaks your data to the world. It's still feels like your old friend, cosy and comforting.
The vast, vast bulk of computer users are more interested in the destination than the journey. They don't really want to have to care what browser or OS or app they're using... They want to manage their finances, or make art, or surf the web, etc.
When the destination is the point, small amounts of asymmetry tends to accrue more asymmetry because it's easier to solve problems if the help ecosystem is larger to address when the tool doesn't work the way the user wants it to.
I wonder how much is end user driven, and how much is intermediary driven though. Is it that the customers are only comfortable with one item in each category, or is it the middle men who prefer to sell things that are all connected by the same platform?