They still could encourage gambling, but someone somewhere judged it's the lesser of two evils.

Among other things, lots of those kids are probably using their phones to gamble way more money than they'll ever lose playing poker with their friends.

Playing poker with friends is at worst zero-sum with limited downside; your friends will probably cut you off when you run out of money and the money stays in your little pool. Betting sports against a faceless profit-maximizing corporation is negative-sum and if it turns into a problem for they're happy to raise your minimum and encourage dumber bets.

Anything could encourage gambling to a person who has a penchant for gambling. Cards and dominoes are no different than anything else that can be bet on, which is pretty much everything.

As long as they keep it in the friends circle, the social aspect of it is going to limit the damage that lousy players do to their wallet. On the other hand, being good at gambling (at least for games that are not designed to give the bank an inherent advantage) requires a good understanding of statistics, which is also useful in science and in life generally!