It’s not a zero sum game but I think maybe we’re using the term millionaires differently.

When I, and most people I presume, use millionaires in casual conversation the reference is to being wealthier than most of society. It’s not usually meant as precisely having at least a million dollars since inflation has made that not a lot of money already since the colloquial use of the term millionaires first came about.

If you mean literally having a million dollars than we can probably just wait 50 years and even the destitute will be able to scrounge around for that much change.