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.