Dragon Quest 11 has a T-for-Teen rating and it's got a literal casino built into the game. Roulette, poker, and slot machines. This isn't even uncommon for JRPGs. Curious how the ratings agencies just glaze over this fact when assigning their scores.
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?
They probably have some checklist which has vague definitions of "glamourising" gambling. I reckon this game unwittingly strays into the red tape in its presentation along with the poker theme (like I've said elsewhere it's more a maths game than a poker game). The music and lights despite being atmospheric and ambient probably have some similarities to fruit machine like environments in the sense the music is repetitive and there is flashing visual feedback.
Edit: Should say it's still B.S. to rate it 18. Just that I can imagine ratings boards can't apply independent thought/logic.