When you're making scripts, you can easily adapt them to be usable with this or that or neither of those. So scripts are very useable by community, whose overall gameplay designs range from negative infinite to positive infinite.
Resources, on the other hand, are different. If I make a set of resources, this set of resources has to be able to be usable by itself, or to offer the necessary amount to be used by people that can't do assets from zero (people that can edit but are afraid of taking the next step because it costs so much time). And mixing resources is bad 90% of the time (this style clashes with this other one). Even when talking of the same artist!
Surely people can make RTP edits or something like that and share them. But for editing something, all you need is to make this graphic to meet your existing design, or your expectations. Any edit-capable person will do it by his/her self with the appropiate basis, and will make the, i.e., characters he/she need on that specific style.
Following the example, you will not make any possible character combination of course. Your best bet is a resource set. Something that exists too (known as character generators, OR just plain pieces you merge on your preferred image manipulation/editing program).
For music the options are way less. Unless you get some samples and merge them by yourself (or take some MIDIs and start bashing some Soundfonts and VSTs like I do!). But I think you need some music theory to back up that kind of thing.
So, why are there more scripts? Because sharing scripts has more sense, that on my humble opinion of course,
Orochii Zouveleki
EDIT: Here goes personal experience. Before, everytime I did some small work I knew I wasn't going to use (or even some that I did wanted to use), I shared them. All of those, never got used by anyone, or not that I knew of. Why? Because stand-alone graphics are never going to be used, even if there were people who did said they liked them or whatever (maybe they lied to me so I felt better :'D -idk ; idc-).