Coinbase is a centralized exchange, the trading does not happen onchain so the trading itself has nothing to do with crypto, it's fundamentally just like a stock exchange. Onchain trading would be using a decentralized exchange, and that's much cheaper now on Ethereum L2 for example (although still in the experimental phase, slowly getting there). Coinbase is btw one of the more expensive CEX, but I guess you're there paying the higher fees and not with the competition, because they're reputable and unlikely to steal or lose your funds, correct?
The great thing about cryptocurrency is you can trade it any way you like. You can take your tokens in self custody. You can in theory trade with a random guy on the street, without any third party involvement and with zero fees. I know a guy who does this because he's worried about a coming police state, so he buys everything with cash during meetups.
I think the high fees CEX are currently charging, which you're right about, has multiple reasons. One is it's a completely new and largely unregulated space. There are a lot of risks, they need to set aside a lot for litigation. FTX had very low fees for example while stealing customer funds to lobby Washington ;) Coinbase is legit but has to spend a lot on legal fees and compliance, because they're in it for the long run. Also a huge part of the reason is surely simply because they can. Crypto traders are making so much money that they're more likely to accept paying high fees than the average stock trader. That won't last forever, it's just because the market is new and volatility is crazy.