If they set up some sorta weekly & monthly & seasonal & yearly tournaments, some people will be very invested (probably). If the tournaments weren't high commitments, that would be fun since there's a end goal of 1m by year's end.

If enough, and if valve does p2p shit well, casuals might also find it enjoyable w/ friends. I really enjoyed fucking around in magic with friends but the cost was too high to continue. Magic Arena (beta) didn't really allow friends to play together either so that kinda fucked it all up for me. I don't know if they will be able to replicate the lunch table phenomenon of physical card games, but that shit is also pretty cool and has it's own motivators.