Lo Celso was also injured many of the times when Ndombele was taken off. I actually can't remember the last time Ndombele completed a full 90 mins. Can you?
How many 90 minutes has even completed for Spurs in total?
Does Mourinho strike you as the kind of manager that makes changes when he doesn't need to? Why does he almost never take off Kane, PEH or Son?
Are you really suggesting Ndombele is unique in the amount of work he gets through in a game? PEH has played every single PL minute this season, Kane has often been our box to box midfielder and never got a moment's rest, and it's not like we don't have a young backup striker in need of minutes.
You're honestly sounding like a conspiracy nut. There's no deep 4d chess going on here, the explanation is simple. Ndombele arrived here unfit, remained unfit his entire first season. He's finally living up to the hype, but for only about one half per game, and for 65m + 200k a week it's just not enough. We need him to not become a liability in the final 20/30 mins of games.