those not available would likely be those that are not really necessary or very useful to most Zenners generally.
I disagree.
Contributions do not exist based on demand nor what the masses deem important, in fact neither does Zen Cart.

Both exist on the whims/interests and goodwill of the developers.

Evidently the originator of any code change thinks that their mod is absolutely essential to his/her site or they would not have done it in the first place. Whether others agree is extremely variable.

Where there is real demand for a mod to overcome the shortcomings of ZC, if you are lucky in has stepped a commercial developer and that code may well be plugin but you wont see in the Plugins section, nor even allowed to be discussed on this site for debatable reasons.

Personally I think it's time this was shaken up with:
- commercial modules discussed, named and shamed to protect the innocent and also make very plain what is lacking in ZC/the masses want.
- the "Plugins" brutally culled, leaving only the well-written ones from reputable contributors standing
- the majority of the current "plugins" reduced to their real status of a set of hacks downloadable from their support thread and so making it plain that all code is potentially dangerous / "as is" and all bets are off. This would encourage people to post their minor code changes quickly with no fuss and so promote discussion and testing in the community etc, all good things.

that's my 10 centimos.