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)
Bitcoin is in a legal gray area. Taxes are not exactly defined for Bitcoin and a lot of people who "trade" stocks nowadays either just buy and wait or they're running bots which do it all for them. They have algorithms, technical analysis they can perform which is more often than not very, very accurate, and there is a lot less volatility which can make or break a trader.
Bitcoin, to them, is something that has massive returns, at the cost of not being able to accurately determine when anything happens and mostly relying on dumb luck to get a good return on market movements, now anyways.