It's definitely a niche thing, but I do see the value. Like I mentioned, I've gone from 1st gen Ryzen to 2nd gen Ryzen to 3rd gen Ryzen on a single X370 motherboard. We've seen benchmarks show that the performance difference is negligible. Sure, I miss out on some new features like PCIe 4.0 and better memory OC, but I don't really need then right now, and more importantly using the same motherboard has many benefits - it's just easier, some of my software licenses (including Windows) is tied to my motherboard, so that saves some time too.
Other practical scenarios would be, one may be cash strapped and need a system urgently, they can opt for a Ryzen 3 or even Athlon APU. Then over time save up and upgrade to better CPU, add a GPU etc.
This is true! I do definitely see the value in longevity of base parts for a system. I still think what AMD managed to achieve thus far was quite remarkable in terms of backwards compatibility!
Absolutely! It'll also likely never happen again, supporting one socket for 5 years is unheard of. I guess a desperate AMD made that decision in 2015 without fully understanding just how difficult it would be.
Oh yes, I doubt that'll ever happen again. But I also think they proved their point well enough too! Intel just launched their 10th gen stuff that, to no one's surprise, requires a new socket. For what is, effectively, a basically unchanged chipset design, more or less.