The removal of SD cards always just felt petty, but at the end of the day, you can either plug in external media, use a wireless hard drive/SD reader, or just access your content remotely on self hosted servers (or use "the cloud" if you must).
Rootability is easy -- the real issue these days is how many things stop working with a rooted phone which makes it much less desirable than it used to be. Though, it's also a lot less important than it used to be, as many of the old functions that required root just don't any more, either because of changes to the system design, or because of workarounds.
I was watching clips of LinusTechTips' podcast, and he said that speaking to people who he trusts in the mobile phone space, that SD removal was primarily because SD flash is worse than the onboard stuff and they lose more customers who complain/think the phone is bad because of the SD card being worse, than customers who wouldn't buy the phone in the first place because it lacked it.
Personally, I think it's a little of both. It probably helps that less customers complain about the SD card not working, but being able charge an arm and leg for extra storage is icing on the cake.
Rootability is easy -- the real issue these days is how many things stop working with a rooted phone which makes it much less desirable than it used to be. Though, it's also a lot less important than it used to be, as many of the old functions that required root just don't any more, either because of changes to the system design, or because of workarounds.