Your concern is a good one and I had thought of it many times, it's the same answer that keeps ringing in my head.

You are judging by the relevance of Bitcoin today, but neglecting the impact of CEX in helping it to have a deeper root. CEX builds businesses and eases around Bitcoin. And I would continue to say that it wouldn't have achieved this popularity and adoption so fast without CEX. CEX is the one that builds the trust of people more on Bitcoin due to the ease of accessibility of their coins and the ability to use them fast and interchangeably within the system. It offers the added advantages that DEX can't offer, which include higher liquidity, zero exchange fee and much more.

DEX would have done it if it has the power. Aside from keeping Bitcoin private and preserving ownership, CEX offer more benefits that people will turn a deaf hear to what you have to say about DEX.