Gambling games are bad for the exact same reasons that grind-based are bad: people play them for the addictive reward mechanisms. If you're not affected by those mechanisms, you're usually left with garbage.

Variable rewards are also the reason why poker is one of the few games with a heavy skill component that can move large amounts of money directly between players; few people are willing to be a sucker. So losing players have to either get something else from the experience, or be convinced that they aren't losing players.

I said elsewhere in this thread that skill-based vs. luck based is a continuum. The most popular poker games tend to land on the sweet spot where "enough luck that bad players can think they're good" and "enough skill that you can actually be good" meet.