Because it's desirable for the publisher? Since, you know, they make way more money that way.
> if MtG uses this model for deck building it sounds like pay-to-win.
It is pay-to-win, up to a point. There is an upper ceiling on how much a top-tier deck can cost to acquire (usually a few hundred dollars, in the most popular formats), and after that point money no longer confers an advantage. That's how it can be a competitive game at all, even when you bring your own deck.
> a blockchain game can just be pay-to-own and play-to-own like most games on the App Store, except the assets assigned to the user is not attached to a single App Store account and do not involve a 30% take fee. imagine these game assets could still be held even if you switch from Apple to Google phone, because the assets are detached from your phone company’s accounts.
Very nice - for the player. Why would the game publisher, Google, or Apple want to make an effort to recognize assets from a blockchain they do not control and do not profit from?