Skill based slots were a stupid idea. This was a case of casino execs totally failing to understand millennials.
The thinking was, "Millennials love video games, so let's give them a video game form of a slot machine, and we will see handsome profits!"
What they failed to understand was the fact that millennials love video games when they can practice their skills at said video games without additional cost. So a slot machine where the house has a huge edge until you get good enough at the skill-based part isn't appealing. The millennials will play once, suck at it, lose money, and give up. They're not going to look at the crude video game embedded in the slot machine and think, "Oh boy, I'm gonna spend thousands learning to get better at that!!"
Also, those machines were not labeled particularly well, so most millennials didn't even understand they were looking at skill-based machines.
BTW the whole nightclub/hip atmosphere was being done in order to make money from the hotel/restaurant/club portions, and not the casino. That's been an ongoing shift in Vegas in general, where they're trying to push for a higher percentage of non-gaming revenue than ever before. I doubt that much will change. However, it's possible that they've determined that the real money lies with the older generations (most millennials don't have much to spend), so perhaps that's why there seems to be a shift to marketing to older and middle aged people again.