Possibly this happened because a) the vendors only offered a micropayment model and b) the product was so popular that nobody pushed back.
That said we can see LLM inference being sold on a subscription basis commonly now (e.g. Claude Code).
You could buy and sell virtual items with a real-world cost far smaller than the transaction fees of a regular card transaction.
Speaking of which - that, to my mind, is the definition of a micropayment - a payment too small to be practical to administer using existing card payment infrastructure. So-called "micropayments" in games have long since ceased to qualify under that definition - they're just "transactions" now.