i dont know if you have ever had a boss that was like mine. You have 2 days to finish a project that really you need 4, so you build templates take others code to get it built quicker if you did everything from scratch you'd get fired and from what i know most developers have similar issues at least some days. when you have such tight deadlines as most developers do, you go to the resources you trust the ones you go to that you know will give you the answers you seek, like this http://www.ascii.cl/htmlcodes.htm I know what it is and what i will get. Codepens dont give you that security they are random and sometimes excellent, but its hard to find the one you want because of the differences between them, usually the code is also to complicated to just slide into your own projects. (these are my opinions granted but i know others feel the same)
Now that knocks out codepens, what about other gsap resources?
when you search for gsap you will get this http://greensock.com/get-started-js, its a good start yet ... no one reads something that long im sorry but its uninteresting , to much text if you are willing, you get to something i use often (that easing box) but thats only if you scroll down a fair distance. Saying that the docs are quite strong. Some people use docs if they must but they prefer alternatives - more interesting things. now the learning center has a few things and i hope it grows but its hidden away hard to find, even then it doesnt consider how people learn to well.
Using this as an example
var tl = new TimelineLite(); tl.to("#green", 1, {x:750}) .to("#blue", 1, {x:750}) .to("#orange", 1, {x:750});
I found this on one of the pages. right well, code is solid but most programmers like to change code to what they need... especially when in a hurry, this code ... it wouldn't be useful in a project... it's unlikely people will move 3 objects like this one after another, yes you can adjust it but then you might as well be starting from scratch, code like this should be something someone might actually use.
what people need and want is something like this http://daneden.github.io/animate.css/ it's simple you get the code you understand and you get elements you need. Then you add it to you application or website.
Modern developers they use the resources they have and gsap has quite a few but they are mismatched they all have good elements but are all flawed somehow, really if you combined them all you would have something truly useful.
im not suggesting we do this purely by ourselves i would like some of the gsap team to get involved, They have something special here and more people need to starting using it,