Creator of Sunshine here.
The main issue I find with my fellow mapmakers is that they're very discouraged from making maps for comp due to the high level of antipathy players tend to have towards them. I've experienced it firsthand - throughout the >2 year development cycle of Sunshine, I've had literally hundreds upon hundreds of people telling me my work is shit, giving me no advice on how to improve it, telling me it's worthless and a ripoff of other maps.
Mapmakers don't want to hear that.
Don't blame us for not making maps - blame the inconsistent testing groups, assholes who will take every opportunity to talk down custom maps without giving any feedback (mustard, I'm looking at you), etc. You can't expect mapmakers to make a perfect map from iteration one. It doesn't happen. Not everyone can be Scorpio. Even Scorpio isn't perfect.
If you want more maps, support map testing groups. Show up to tests. Support people giving constructive feedback, and get rid of assholes quickly. A few weeks ago some map pug group ran Edifice and I stepped in to listen, first thing I was greeted with was a group of people who ran around the map and proceeded to shit all over it. They didn't give any constructive feedback. They just said over and over again how terrible it looked.
Don't blame TF2Maps.net for not wanting to map for comp when every time they try to, they're greeted with people telling them their map is shit.
I'm making another 5cp map right now (see: http://tf2maps.net/threads/wildlife.23624/ ) but I'm hesitant to bring it over to comp. I don't think people will give me good enough feedback for it to be worth it. Can people change enough for mappers to care again? I don't know.
Sunshine was a huge step for custom maps and I'm currently in the process of writing a "5cp guidelines for comp" sort of article for tf2maps.net, so as to maybe encourage people to get back into comp. It can't be only the mapmakers effort, though. The community as a whole needs to change their outlook. Embrace maps like Sunshine and Logjam, don't constantly shit all over them without actually providing feedback. Mapping takes time, lots and lots of time, and mapmakers like me and Hyce don't get paid at all for the years of work we're putting into our maps. I have not got a single bit of monetary compensation for sunshine, I spent tireless hours over 2 years putting it together. Don't blame us. We're trying.