It's easy to see why your argument is wrong with a simple hypothetical: what if they were still making DDR4 today? Would people still buy it?

The answer is an obvious "fuck yeah", even if you ignore the DDR5 price gouging. People will buy it because people still have DDR4 hardware, and that hardware is still extremely relevant.

So if there's a market for it, but none of the suppliers are trying to sell to it... Wtf is happening? Basic capitalism logic says any rational supplier would sell DDR4 for easy profits, meeting an unmet demand. That it isn't happen points to some kind of collusion, IMO.