Nah, being unable to pause just means they get way more minutes of viewing when people put down their phone to do something. It just sits there and plays, earning that sweet sweet ad money.
This might not always stop playback, for example with YT Premium, I think it also applies to shorts, maybe only when in PiP mode? I can't recall, but I'm pretty sure, I've encountered it, somewhat inconsistently
YouTube Shorts don’t have background play/PiP, at least not through the regular Shorts player. It is possible to get a Short pulled up through the main video player because each Short actually has a page you can access by just replacing /short/ with /v/ in the URL, and that will have background play and PiP if you have these enabled.
Tapping some URLs will inconsistently get you to the page too without having to do any URL replacement. I don’t think there’s any intended logic there, just some bugs in the way URLs get handled hopping from social media app to browser to social media app since most of them try to keep you silo’d in.
I can get PiP from shorts 100% just tested it (At least in MIUI, maybe it depends on the implementation)
What you're describing is a bit different(It's probably implemented like this because old videos that weren't initially uploaded as shorts were absorbed into shorts if they fit the correct criteria)