How exchanges/brokers/traders of non-crypto "stocks" have not invaded crypto platforms yet?
Crypto usually generates better profit (and better chances) than most stocks.
How people who live from stock-trading (e.g.: companies) have not invaded crypto yet?
(If we look at communities' sizes, their size is much-much larger)
They haven't invaded crypto yet because crypto is a significantly worse investment than most of the stuff that wall st big money invests in. There are opportunities out there with just as much potential upside, and significantly less risk. Crypto is very, very risky. Just because it has gone up recently doesn't mean that it is a reliable investment.
Furthermore, bitcoin has high transaction fees that would not be friendly to people trying to trade tens or hundreds of millions, or even more, at a time. Percentage based fees for transactions of that size would be completely unacceptable.