Makes sense going for his 4th Vuelta win. Maybe next year he can do the Tour de France again all though I feel he needs a bit of luck winning that one. There always seems to be someone better then him it either being Pogacar or Vinegaard.
It's just been the crashes really. He has every right to co-lead jumbo at the tour, the strongest team. He would even be more likely than vingegaard to win over Pog IMO if they all get the the end safely as he maybe has a tiny edge in TT and is tactically the guy to sit on and finish faster while vingegaard attacks (think Thomas '18 with vingegaard in the froome role).
Honestly if jumbo only cared about the tour (they obviously don't and now could conceivably sweep the GTs) they should have had him focus so they can double team Pog again, I think his absense really hurts them.
I think Le Tour never was in Primoz's schedule since winter training. It was all about Giro d'Italia and now they may have tested him both physically and mentally and Jumbo have seen no point to include him in the Tour's eight. Just guessing here, but if some health issue happens to one of the eight selected then maybe Primoz could replace him.