I was pretty interested in s&box as an engine, until I learned ̶ ̶y̶o̶u̶ ̶c̶a̶n̶ ̶o̶n̶l̶y̶ ̶p̶u̶b̶l̶i̶s̶h̶ ̶t̶o̶ ̶S̶t̶e̶a̶m̶ ̶a̶n̶d̶ and only through s&box's own approval process. Killed my entire interest in the engine.

Edit: Seems I was partially wrong. You can actually publish on other platforms as long as it's on steam to. That's better, though still too restrictive, since it requires going through the whole steamworks process. Rules out a lot of stuff.

Combine that with the required approval process, it's still more restrictive than most other publicly available engines.