mastercomsBarytaQ80% of the point to online card games is to get kids to buy packs, there's no way they don't have MTX in this.
When has Valve ever done the norm? MOBA games had buyable heroes, and other paid game mechanics, but not Dota. FPS titles had paid map packs and weapon DLC. But not TF2 or CSGO.
I'd say nothing about MOBAs or FPSes require paid DLC or locking content behind paywalls. It's just something that was introduced by some games, well after the moba or fps genres were made, to get more money.
Trading/collectible card games kinda require that, since collecting them has always been a core part and one of the more fun aspects of the genre. You could have other ways of getting cards; free packs, just getting cards randomly, etc. but people will still want to be able to buy them and there's no sense in stopping them. Or have every card available for everyone, but that ruins half the fun in it.