I've had MUTV for 10+ years now, and watch every game(most more than once), so i'm not just going off reports, and i'm not suggesting SAF was there at every reserve/u23/21 game because he wasn't, and less so towards the end, but there was always some first team representation, either Mike Phelan, Rene M or Carlos Q keeping their eyes on the players giving them encouragement that if they performed well it would be noted, similarly with LvG, if he wasn't there Albert Stuivenberg was - with Mourinho it's just not happening or doesn't appear too, though maybe the MUTV camera crew don't know who they are looking for, but I doubt it.
I remember a few years back where SAF in a post-match interview(we'd just won an important League match) on MUTV asked the reporter how the 'A' had got on that morning, and on hearing they'd lost he was absolutely gutted, you'd have thought somebody had just told him his dog had died, I just can't imagine Mourinho asking, or being bothered.
On the rare occasions the reserve team struggled SAF was always open to first-team squad players playing down a level to help out, even if it was only for a few games, yet now it just doesn't happen, there were times last season(under Warren Joyce)where it was obvious the team were short on confidence, just imagine the lift the players would've got if a few experienced players joined them, it didn't have to be long-term, just enough to get a few positive results, as it was Warren Joyce and the players just went through the motions, and it seems to have continued under Sbragia(a strange appointment)this season.
We've got the situation this year with Mkhitaryan and Lindelof(and there were others last season), both talented lads not playing at their best level, instead of leaving them on the outside to stew, why not stick them in the 23s for a couple of games to get their confidence back up, i'm sure the young lads would have benefited from having their experience on the pitch. It only needs a couple of wins, then the confidence is back, they're not the most talented bunch we've had but they are a lot better than the League position suggests.
I don't recall crediting Mourinho with the 18s doing well.