Yes, but that would be boring. Which projects deserve to be the chosen few? Who wants to play a campaign they built more than one someone else built, and that they've never seen/played before?
It'd be up to the individuals to decide what they'd focus on. The point still remains. The more projects one has joined into, the less productive one is. This is generalization but it is mostly very accurate one. One because team's productivity is low, the longer each project takes to finish.
If a person has joined to two projects, has approximately one hour per day to spend on modding. How much he spends on each project? Less than 30 minutes because he needs to keep tabs on two projects, communicate with two teams, etc. And as we know, human's aren't exactly made for multi-tasking. Now, take the same person and have him join to two more projects, so now he has four projects. You're lucky if he's able to spend 5 minutes per project.
Great, now what? The person has to choose which project to focus on. What happens after a while is that the person starts feeling guilty for giving other projects little focus. So now he's again trying to fiddle between multiple projects, usually with little success. If the person has not discussed the situation with other team members, he's eventually bound to get some pressure on himself from said team to get things done.
Rinse and repeat until you have burned out person who has steadily lost motivation.
Not exactly a success story here, is it? Now, focusing that effort and time on one, maybe two projects at a time is time and effort much better spent. Not only it is more efficient use of one's resources, it also more efficient for one to handle psychically.
So I'm not going to back down from saying it as many times as necessary. Joining multiple projects (or at least more than two) in almost all cases is idiotic.