Then sorry, but you are blind.
Delays, expenses, broken implementations of CPU support, people flashing the wrong UEFI and then getting zero support because it's a beta. You think the customer paid for that level of support, but the truth is that when someone bought a $100 motherboard, it probably did not cover the expenses involved in supporting all these chips! OEMs have been feeding off Intel for years, and now they can't do that in the DiY sector since AMD is dominating sales.
Can you get Chaintech, DFI, Foxconn, PC Chips, or Abit-brand motherboards anymore? No? There are reasons for that.
When a $100 board (or any board) does not get any future CPU support it is because is EOL, this date is pre-defined from the start with your scenario in mind. There is not a single 400 board that is EOL, bring me a single example, you are unlikely to find one. This is in part due to B550 being delayed, but thats not the customers fault. So like it not, they are kinda forced to do it.
As a example i can give you Carrizo APU on FM2... Premium A88 boards never got support, because they were EOL, yet, some cheap ass A68 did, price does not really matters, it matters if is EOL or not. Dont be suprised if A320 ends up getting better support than all other 300 series boards.
And look, no warranty covers damages from beta bios, if someone download and flash a beta bios that has the proper warnings, thats no OEM problem. Still brands like Gigabyte will fix it for you as long you still have warranty, since bios flash is included in the "friendly" support.
At any rate, everything you said only applies to 300 series boards, that are unlikely to get Zen 3/Renoir support outside some risky beta bios.
Anyway, you want to know what a REAL support nightmare is? Cutting cpus off in the same socket.
Intel shenanigans with 6th/7th/8th/9th on 1151 socket was a NIGHTMARE, for us, the people that actually have to sell those, even today the averange joe still do stuff like buying a 9100 for a H110...
Cutting 300/400 off Zen 3/Renoir is... its going to be a dissaster, but at least something i can control with bios and a little testing now. B550 whout old Ryzen support, im going to have a ton of returned motherboards if no support is given. OEMs work closely to us, Gigabyte and Asus, mainly, and they do understand that. And i dont think it is that different in the rest of the world.
Look, if you want to do that, change the socket, please. It is still a mess, but a cleaner one.