If you create 50,000 coins (or shares, or whatever), and sell one for $200, then you have a "$1 million market cap!", but you actually got $200.

For a scammer behind a coin with a $50m market cap to have walked way with $50m, they would have needed to have sold all the coins at that valuation. In some cases, this may have happened. In many others, they will have sold some coins at that valuation, and others at lower valuations as the coin collapsed. In a few cases, all the transactions may have been "wash" transactions (aka, selling a coin to yourself under a fake name), and the scammer may have received nothing.

It's hard to know how much a scammer profited without digging into it, especially in the crypto space where wash transactions are so easy to get away with.