Inter can affort it too. Chinese man have many money..

and he can spent it
It is not a problem of being able to afford it anymore - many rich owners/clubs can afford top players. Even though FFP is a joke, the clubs still have to work under some rules and no club can pay Messi's release clause and still fulfill the FFP requirements - not even close.
Man City got away with cooking the books already this year so they will not want another investigation.
Buying Messi is impossible right now - unless Barcelona lower their demands to something under 100 million. Which they said they will not do.