Moreover, despite compulsory KYC hassles and failing a number of times in the process, centralized exchanges are not losing popularity. Is it only because DExes don't support fiat? Or is it simply because CExes are generally better? Or perhaps people aren't really interested get out of fiat altogether?
CEX are proper businesses set up with proper physical legal addresses which you can file law suits against should they wrong you.
DEX are random individuals hiding away behind tor and proxy and virtual mail/PO Boxes which if they should wrong you, your just lost and no way to claw back anything
CEX are also easy to find on the internet, and have had years of reputation.
DEX are hard to find and even harder to trust
..
For many years, DExes are left behind by CExes in terms of volume.
dont worry about volume
when an exchange does a arbitrage. it may only have say 100btc involved. but when it sidechain swaps to another exchange, plays on that exchange and then tethers back to then buy coin and repeat every minute. that 1 allotment of 100btc can be seen as being 10,000btc volume due to arbitraging 100 times a day. even though its only 100btc being spend repeatedly
its like looking at bitcoin network 'btc transaction value' per day.
when people re-spend the same allotment of coins by spamming the network EVERY BLOCK that single coin. appears as 144 coins a day.
in short.. volume is meaningless as it does not explain who/how much//how often individuals actually spend individual funds
even things like exchanges just moving funds from cold to hotwallet where its not 'spending' but just organising its own wallet holdings. it appears on the network as thousands of coin 'volume'
EG the 'whale alert' twitter bot keeps announcing whale spends of thousands of coins.. where reality is its just an exchange organising its custodial funds.
so dont put too much thought into the value of the volume statistic