Well there’s a few reasons:
1- With the new salary structure if you have young talent it will behoove you to trade 2 for 1. Bc eventually even a 3rd option non-star is gonna earn the max (Giddey, jaylen Williams, Mobley. Houston in particular is about to have potentially 4 players who will all want max deals).
2- With those 3 teams in particular: Chet holmgreen is probably just as much a risk as Zion. Jaylen green is already a questionable fit and again they have a ton of talent they as Soo as next year it’s gonna be TOO much talent. And Mobley might already be pidgeon holed to just a defender. Another year as a big zes option his value could plummet
3- The upside
Garland-Mitchell-Zion
SGA-Giddey-Zion
Harden-Porter-Eason-Zion-Sengun