At this point people who are in the Samsung ecosystem
like the Samsung UI. The Galaxy brand is arguably just as valuable as the Android brand, if you want to be real about it. Samsung absolutely would have sold their own SamsungOS-branded phones.
The first truly successful Android devices were the Motorola Droid and the original Samsung Galaxy. Even back then, in the Android 2.X days, they were making modifications to the style of Android, similar to the way Samsung and HTC and others had similarly customized Windows Mobile in the pre-iPhone smartphone era.
Android managed to get a stronghold thanks to Google’s aggressive investment and the fact that they didn’t charge OEMs a royalty to use it (which Microsoft did and Symbian did. Also, neither Symbian nor Windows Mobile were at all competitive to iOS and Android was after Google pivoted post-iPhone launch) and the fact that they let carriers and OEMs do whatever they wanted to the interface and add whatever bloatware they wanted.
It wasn’t until well past the success of the Galaxy line that Google started to try to rein in the diversions and UX forks. And Samsung, which has a UX that at this point many of its customers prefer, has received a light touch from a lot of these attempts because they are consistently one of the largest Android OEMs.
Android largely has a userbase because Google let the OEMs do whatever they wanted, similar to what Symbian and Windows Mobile had allowed before.