I don't consider this a **Linux** assurance, it's one offered by individual distros.

Arguably the need for every Linux to support everything from Celerons to Strix Halos is a bug, not a feature. There is nothing wrong with having both distros that abandon 32-bit CPUs (ie. CachyOS) and distos that cater to them (ie, Puppy). It is no coincidence that the ones that perform best on newer hardware (CachyOS and at one time Clear Linux) are that way because their attention can be focused on the modern stuff and won't need to support every PC ever made. Every distribution has finite resources, so priorities matter.

What's important is that Linux-the-kernel needs to support a broad range of gear but distributions need not be constrained that way. Tools, filesystems, compile flags can and should be optimized to the extent they can. There are certainly some distros -- Debian notable among them -- that cover as wide a range as possible. But a one-size-fits-all approach is less valuable once you know what your target hardware is and can choose a distribution to best match it.

This is indeed one of the main parts of the answer to "why are there so many distributions?".