To me, casually watching the various Pi related forums, it appears that many hobbyists that might have used the Pi 4 for an interesting project found other interesting things to do using the Pi Zero and/or RP2040.
For example: "Raspberry Pi Zero 2 W with Ubuntu Server 21.10", "Kali on Raspberry Pi Zero".
Linux on a RP2040 appears to be a work-in-progress. Is RP2040 too small? Maybe wait for the next generation of RP2040?
Might be a matter of memory. The RP2040 itself has 256KB of SRAM and the Pico and Pico W add just 2MB of on-board memory. That's pretty tight to host an actual operating system...