The majority of Linux distributions out there seem to be over-engineering their method of distribution. They are not giving us a new distribution of Linux. They are giving us an existing distribution of Linux, but with a different distribution of non-system software (like a different desktop environment or configuration of it)
In many cases, turning an installation of the base distribution used to the one they’re shipping is a matter of installing certain packages and setting some configurations. Why should the user be required to reinstall their whole OS for this?
It would be way more practical if those distributions are available as packages, preferably managed by the package manager itself. This is much easier for both the user and the developer.
Some developers may find it less satisfying to do this, and I don’t mean to force my opinion on anyone, but only suggesting that there’s an easier way to do this. Distributions should be changing things that aren’t easily doable without a system reinstall.
I think your focus is on ease for distributors rather than ease for users. Unless they had a series of checkboxes to choose your flavour, most won’t like it and it won’t gain traction.
It’s a bit like “why cannot people cook food in a restaurant to their liking rather than a chef doing all these meals and variations?”. People just wanna eat.
If you’re basing your distro on another distro, you’ll need to modify your dependencies to fit the existing packages anyway. It seems like the only difference is which repo the additional packages are being fetched from.