Why? Because as a full-time developer wanting to do a side-project, you need to build what you can in a short time frame, with minimal maintenance, and without worrying about hosting costs.
And you actually want users and minimal marketing.
These are the smallest true solo dev projects you can build I think.
I’ve built 10 in the last year (mostly for fun) monetised one, and have a flagship extension I’ve just released that I expect to do well [0]
Ask me anything about chrome extension development!
Though that being said, API-only is also a good gig.
[0] - https://chromewebstore.google.com/detail/design-copilot/hgal...