Because he's a rider who doesn't race much, like the riders of the late 1990s and early 2000s. Perhaps by racing more, he'd be less competitive in the Tour.
Riding the Giro-Tour is complicated, and next year he'll turn 30; he can't wait any longer, or Lipowitz or another young rider could surprise him any year.
He'll be regretting giving the Vuelta to Kuss. Now he has to fight for it with Pogacar, and in the future there may be stronger young riders.
It was crazy to give a GT, even to a teammate. They're hard to win. Pogacar wouldn't have done it.