Actually you can use them as external displays but requires some hackery. See https://ohmypizza.com/2023/04/converting-a-5k-imac-into-an-e...

But yeah agree entirely there. When upgrading from my somewhat cranky old 5k iMac a while back, I decided I'd never buy another iMac. The 24" was out. So I bought a Studio Display and a mac mini. At least I can upgrade the computer separately, which has happened already (M2 mini -> M4 mini). I expect the Studio Display to last a long time as you can actually buy parts for it.