This is the part I can’t figure out. It’s not just indie games: ages ago, Pokémon dropped the casinos from their games specifically to avoid having their age rating bumped in NA and EU. So clearly they sometimes account for gambling in side content. But somehow other franchises have kept them in, and aren’t suffering.
Does it just depend on whether or not the particular person assigned to review your game is a hardass about particular things?
If you search for “poker” on PEGI’s site, it seems that many games which are actually about simulated gambling are rated 12 or 16. They seem to think Balatro is more likely to expose children to realistic gambling than, say, Prominence Poker or Pure Hold’em World Poker Championship, which seems completely bizarre, given that those games are about playing poker and Balatro is a fancy kind of solitaire with no betting.