Cookieless is the default here, and a decision there. Matomo can be configured to run without cookies; out of the box it uses them, and the configuration is on you. Skomi stores nothing on a visitor's device unless you deliberately turn that on, so the safe state is the one you get without doing anything.
A small script. Ours is 11.7 KB gzipped, and here is what is in it. Matomo's does far more on the visitor's machine, which is the same reason it can do more.
Less to learn. Matomo has a report for nearly everything, which is its strength and the reason people bounce off it. Skomi shows fewer things and expects less of you.
Feedback is part of it. Boards, voting and a widget, on the same account.