As a sixth form teacher, I actually think it's the latter. 'Lower ranked' (note speech marks!) unis start from a starting point of having 'entry requirements' that really aren't that far off 'middle ranked' ones. To give an example, my DS has an offer of BBC from Aberystwyth and form Portsmouth. I expected the gap to be wider (and there isn't even a gap!). DS (a BCC student on a good day!) didn't really find many unis that actually claimed to take students on BCC/CCC. But he has applied anyway : the school has predicted him BBC (generously). he has two UiFs from unis that otehrwise want BBC or BCC. If he takes those he wil probably in the end get BCC or CCC, maybe even a bit lower.
I am not sure I am being all that clear: I did have lots of students last year that went to uni on UiFs. None of them got stellar grades (apart from one boy and that was a top university) but tbh they weren't going to anyway. And , it was better for their MH and stress, definitely as with a conditional they would always have been skating on thin ice.
What I don't know is how they are getting on now, mind.
People don't tlak about clearing in the same way. Yet, I had a girl go off to uni, having failed to get her BBB and BCC offers (she got CCD). Arguably, she is as poorly equipped for uni as those who got those UiFs (and got slightly better A Level results). I have caught up with her and she is flourishing.
The students who really don't work hard at A Level are the ones who have no plans for their futures at all (mainly boys!) who generally have zero motivation. They bomb their A Levels and then don't even have a good starting platform for any future change of heart.
What I don't like is the bribery element of UiFs. Much prefer straight unconditionals.