"Make your own kernel" is a thing-in-itself, and "runs on <X> hardware/VM" + "provides <Y>-like API for programs" are tangible, concrete goals to aim for, even if you personally don't like the <Y> API or the architectural choices it implies.
To give an analogy: https://www.nand2tetris.org/ is an amazing learning experience, even though games other than Tetris should and do exist
Personally, I like the AROS project, aiming to provide an operating system that implements the AmigaOS APIs and runs on many architectures, but lots of users are interested in running it on 680x0 Amigas and spiritually-related PowerPC devices: https://en.wikipedia.org/wiki/AROS_Research_Operating_System
It's OK for programmers to write a thing just for the learning experience. If it gains adoptees, that's a happy accident.