Because Dele's success was -> very good first season, brilliant second season, still good third season, mediocre fourth, mediocre fifth, can't get in side anymore sixth. To your point, this was a "period" of his career, it would be the same as arguing for Lamela as the attacking player that was at Roma (that player doesn't exist anymore). And if I wanted to get a jab in, he was part of the team including Eriksen that when it really fudging mattered (your challenge for honors statement), didn't turn up
This unfortunately is not a unique thing with brilliant young British players, raw talent gets them to top level, then when the need to work even harder, adapt to the changes others make to counter, work on consistency, they fade. Dele needs to be super careful the highlight of his career isn't the player he was at 21.
We covered this in earlier conversation, the only upside Dele has right now over those players you think he is better than is "potential" goals, which he hasn't produced in 3 seasons. He is not a more rounded player, all three of the others probably add more defensively, Lucas/Bergwijn add more pace, Lamela adds more bite/leadership, probably a better passer as well.
You are confusing people not "liking/appreciating" Dele with the fact that most people see we have a very pragmatic manager and from a pragmatic point of view, Dele hasn't earned the right to displace any of those front three and isn't likely to.
I don't see Jose going anywhere soon, and I'm not seeing Dele react in the way that would get him back in side (maybe he will, Ndombele looked gone for a while). Said it a couple of times before, if a PSG came in for him in January and we could use that money for a top level CB or a PEH backup .. I'd take it, and I think most everyone would and could be a good thing for Dele.