According to public statements by the execs at Rpi, the availability issues are due almost entirely to unexpected new demand exceeding their planned production

According to public statements by the execs at Rpi, the availability issues are due almost entirely to unexpected new demand exceeding their planned production volume (which they claim was quite large and scaled up from previous gens). They report their suppliers have been delivering their parts orders on time and RPi is shipping the full volume of units they always intended for 2022. They are just getting bought up at a much higher rate than expected. They also say some of the issues in buying single units through online consumer retail channels is because RPi is prioritizing filling advance orders from volume integrators. I have no idea the accuracy of what they're saying but fulfilling advance commitments from volume integrators first makes sense as those are long-term customers who are counting on the orders to ship their own products. Shorting those orders would be fairly disastrous as it flag RPi as an unreliable supplier reducing future design wins.