Was looking over the long list there it seemed like most of them were "nice-to-haves" and not really crucial. Some of them definitely nice to haves, so maybe that's why some things often are left out.
For example: "Stop all timers", nice to have if you use a lot of timers. If not just copy the action and stop them one by one does the same thing. Or if you have many, save them in an array and loop through the array to stop them all. Probably easy to implement, but why bother?
If something makes it in or not may also depend on how likely it would that suggestion would be used, or if you can do pretty much the same thing already, but there's no specific action or condition for it.
Hopefully there will be more time and resources for more "nice-to-haves" in the future, but I think they will get a LOT of requests to make scirra maintained versions of C2 plugins that are no longer supported in C3, where the plugin maker moved on to other things.
Edit: Some if them seemed pretty impossible also like this one for example:
Sprite
Add frame - Add a blank frame to a sprite
It's probably because spritesheets are created on export, and you can't really mess with it after that point, without screwing something up. You cant recreate the spritesheets in runtime. You probably also had to specify the size of that frame, at what index, timing for that frame, imagepoint location, etc etc. even if it's a blank frame 100% transparency, why would you want that? just uses memory. If really needed ..Add a blank frame before you export and set that frame when needed.