I'd have just as much issue with BobStaffer exclusively taking Nick out to the gun range three days a week on his NPC for plot RP and denying that route of play to anyone else as I would if he was TSing Jane three days a week for plot and denying that route to anyone else.
It's basically elevating those people to a level no one else can ever have or hope to have and giving them access no one else can achieve. Giving them a window into plot that no one else can get to.
It just so happens that nine times out of ten, exclusive plot opportunities like this occur in relation to relationships. Other examples might be some esteemed leader taking on a protégé under their wing. That'd also get the side eye and cries of favoritism and the 'Why do they get this inner path to plot that the rest of us don't?! What did they do that's so special to make them an A-lister on the game while we're all just B-listers to look on while they take center stage?'
And part of it, too, lies in how the players handle it.
How often do we see those players stop RPing with the rest of the player base? How often do they start RPing more and more exclusively with Staff NPCs or just their BFFs where before they might have been more social? Sure it might be intended to 'okay you got the plot from me, Staff NPC, now go share it...' but then they go RP with other NPC, then three others,and only two weeks later do they RP with their besties who RP in a big circle for the next four months and outside of that little group the player base doesn't get that plot thread that the super special scene 'handed out' until nearly half a year later.
That is why people chafe at the idea. Because by the time they, the not-center-cast get to it, it's been picked over, investigated, maybe even solved and everyone is on to the next.
So IMO players who get these lauded spots should maybe feel some of that obligation to get out there beyond their usual circles and share and Staff should make sure they find other venues to share the plot to make sure it gets out, too, rather than just hand it to one singular person (even if they intend / hope that person spreads it because usually that spread takes many months and is what leads to people feeling really left out).