If such blockchain would be truly distributed (a-la Ethereum or BTC) then it's bandwidth would be atrocious for an MMO, or it would require some insanely powerful and centralised nodes to handle this, or it would use some L2 solution which would mean a lot of exploits and bugs in the game due to async issues.
Or the the blockchain would be centralised and so useless.
Or the the blockchain would be centralised and so useless.
This idea fails even in the abstract.