the reason for your question is because the centralization exchange (cex) first appeared before the Decentralization Exchange (dex), if if first the DEX appeared first I am sure many people would prefer DEX over CEX now,
if DEX is already many and famous then I'm sure many people will switch to DEX later.
I agree with you! DEX came later, so, people picked the Centralized exchanges as it came first! But DEX will be more popular than Centralized exchange gradually! Because centralized exchange has many issues like the hacking problem, fake/bot volume, lack of liquidity, high listing and withdraw fee and so on. Where DEX is almost hacked free, not much fake trading volume like CEX and withdraw fee is near zero and token listed fee also reasonable.