If you need to upgrade your motherboard to upgrade your CPU it should be viewed like swapping console generations. I don't know in what world you would need to be frequently upgrading your PSU especially considering the tdp of new cards, e.g. the 4070 super that recently released, is more efficient than 3000 cards making PSU requirements less as you upgrade parts.
You're incorrect about needing to upgrade every few years considering that the 2070 Super, which released before the PS5, is more powerful than the PS5. If you bought a 2070 super in 2019, you are perfectly capable of playing every game released on the PS5 gen, on high most likely, at 1080 60fps. It's been 5 years since that card released, still works fine.
But again the argument wasn't that you didn't have to spend potentially more, it was that it doesn't cost 2k. If you build a PC for $500 and then in 3 years spend an extra $500 on a new GPU (I think the 7800XTs are around $500 USD) that's half of 2k and a 7800XT will play probably all the PS6 gen games at 1440 ultra.