> Couldn't you say the same about penny stocks?

Sure, but there are also laws and regulations that limit what you can do with stocks on a real exchange: https://en.wikipedia.org/wiki/Microcap_stock_fraud

> won't this problem go away as BTC gets more popular?

Maybe. It would have to get a lot more popular, and a lot more legitimate and regulated. At that point, it's lost all the cyberpunk appeal, and it's just another speculative asset.

Regarding penny stocks, this does happen all the time, although its expressly illegal (look up boiler room scams).