Stock trading is cheap for a variety of factors that's not applicable to crypto (eg. payment for order flow, stock lending [1]). A stock brokerage can also skimp on security because the legacy financial system has an undo button for oopsies. Finally, a 0.2% fee is relatively competitive with a "reasonable" commission of $5-10/trade (the going rate before brokerages became commission-free) as long the trade is below a few thousand dollars.
[1] https://news.ycombinator.com/item?id=20276551