There were just too many software applications that were designed for raspberry pi 4 (NAS, media servers, btc nodes, console gamimg, etc) That's why the buy pressure remained so high, and thus they did not have any incentive to upgrade to a newer version. They did make a great contribution to SBC culture. However, those excessively high prices for 4 full years will be their doom.

The pressure to copy a raspberry pi 4 was too high and so now stronger/faster products are being produced by their competitors at a cheaper price, both copycats and original legit stuff. I don't see raspberry pi being the king of SBD again, ever.