I think typical front end developers (or the managers they report to) don't really know what smooth UX is. They keep reinventing things like scrolling.
There's almost no HCI or interaction design in what passes for UX today. They are mostly - probably 90+% of them - visual designers who have memorized some canned responses to use when asked why they aren't doing basic things.
Seriously, anyone who things software as a discipline is bad, well, they're right, but they have no appreciation for how appalling "UX" is today vs even 1990.
I think typical front end developers (or the managers they report to) don't really know what smooth UX is. They keep reinventing things like scrolling.