I hope it's something juicy and nefarious but probably just having a constant supply of tourists with money to spend, looking to be entertained has more to do with it.
If they can use Golden Knights arena for basketball (in the same way the bulls share with the Blackhawks) you don't have to build a new stadium, which would be a huge cast reduction for a new team
I get people want the Sonics back but I'm in the minority of being opposed to expansion. There are enough bad teams already and not enough talent to go around. Every team has between like one and four guys who shouldn't be in the league, now you're going to add another 30? There's already a huge lack of depth in the league. I don't think it's going to ruin the league or anything but you're literally lowering the talent threshold.