I would love to know how much each product placement in a movie cost, how much some shady third-party paid to have their bloatware installed on all new laptops from a particular vendor, how much it cost to set the default browser, how much a TV manufacturer was paid to include a "smart TV" device in their product, etc..
I bet it's not even any substantial sums, just enough to get some beancounter to push for it.
Such a shame because the hardware is nice.
The idea being that if all phones ran the same software no one would choose their phone on brand but rather on what particular phone was best suited for their needs.
But that's not good enough, manufacturers create a custom feel solely because customers will get accustomed and need to relearn if they choose another manufacturer.
It doesn't matter if their software is worse than stock (and they all are (much much) worse), the only thing that matters is that it is unique.