I agree with Jump, I see absolutely nothing wrong with a restricted license, and I also think you've made an unfair assumptions that everyone is  "giving back" when they give stuff away.

There's also a number of reasons why some people might not allow commercial that I'm not sure you've considered.

1] There's cases where the software someone uses restricts the creation of commercial work. Examples being academic software, and some software that has a "free for non commercial use" license. If someone were to create something using software licensed as such, it may prohibit them from selling what they've made, but not prohibit them giving it away. Were someone else to use the item given away  in a commercial render, it may well be a violation of the original users software EULA, and may possibly have legal ramifications should that ever come up.

2] Another situation could be that someone's just completed a project, commercial, or a short film of their etc, and once they're done with said project they've decided to release their assets for free. Those assets might include some props, or sets, or even unique characters they've come up with.

If its someone's personal character that they've been developing for a couple years, while they may not mind you using it for your own personal renders, I can certainly see where they might take issue with you using that character in a commercial render.

Also, if they're assets developed specifically for a commercial project, depending on exclusivity or something, the client may not mind those assets being released for free use, but may not like the idea of something they contracted you to make for them appearing in other commercial renders.

3] As I mentioned before, not everyone is necessarily "giving back to the community," I'm sure there's plenty of modelers out there that may well never have "dipped their bucket" into the pool of free stuff as they've always chosen to model their own stuff, and it may well just be a case of them having no further use for what they've modeled [this may well tie in to either of the above reasons as well], so rather than leaving it to collect cyber-dust on their harddrive they see it best to put it up for public consumption.

4] Mr Sparky makes another good point. While there's often little issue with giving away and personal use of copyrighted assets, such as fan art, not everyone realizes that it can't be used for commercial work, and thus it certainly needs to be restricted.

I can't agree with you point about money being tight as a reason why free stuff should be unrestricted. It could be just as easily be that the maker of the free stuff is tight on cash themselves, yet still chooses to give away assets without asking for compensation.

I agree fully with what Jump, and with what Mark and svdl have posted while I've been typing. Going back to one of Jump's points, I see absolutely no problem with someone who's given something away that they very well could have charged for, and in return asking that no one uses said item to make a profit for themselves.

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