While you PLEBIANS engage in ladder play, I enjoy sitting back and enjoying some custom games for the variety therein ;). Unfortunately, compared to Starcraft 1 and Warcraft 3, the use map settings scene seems not quite dead but damn is it limping bad. Is there any particular reason why this is happening? After beating the campaign I got into UMS maps pretty hard and had a good time, especially with the new rage tug of war style maps, but inevitably I petered off and kept taking semi-long breaks (because I got bored with the same map selection). And now, each time I come back I hardly see anything new or for that matter, new and fun (I have very varied tastes so I'm not being a snob either). The RPGs are decent (all 2 of them) and stuff like the capital ship space battle are pretty good.
I'll throw out some of my own things here, maybe some people can confirm if they are accurate.
1). The "popularity" system seems to really lock in crap to the highest levels and people hardly play anything either. Then again, when I do a custom search its not like people are missing out on anything either. When the map tools were first described and all the early examples we saw I'm sure most of us were blown away and now not so much.
2). The NA/EU divide, where we can't share maps or something? I don't really know about this one, since it seems like a really shitty reason why we can't have cross pollination going down. I'm not asking EU or NA mapmakers to buy a second account but holy shit it can't be that hard to find ONE trustworthy person and upload it to the respective community?
3). The map marketplace. I recall seeing some very high quality mods and even total conversions going down which supposedly would only be happening when this happens, and we haven't heard shit about it from Blizzard. Are some map makers holding out on purpose for extra dosh or out of necessity due to file size limitations on a grand scale where we get jack squat filtering down?
Those are the three major things that I can think of and if anyone can shed some more light on any of them or something I didn't mention please tell us. I would love for the UMS scene to expand and for the really high quality stuff to start rolling in.
The insult to ladder players does not have much arguments to back it up as the staggering majority of custom maps doesn't come close to the Starcraft 2 Melee gameplay.
Aside from that there are some easy yet sad answers to your questions:
1) Popularity system, along with missing lobby browser, no chat channels, etc. Killed a lot of the scene off in WoL already. Nowadays it got a lot better but there is just so many bad maps you have to go through until you find a good one.
2) People simply have to upload it to two servers they could do it themselves I don't really see the problem here. It is just a bit inconvenient for the author.
3) There were and are some good custom games still floating around but those that get taken over often get developed into oblivion and people lose interest. I don't think people hold their projects back deliberately. You also have a limited filesize which further gets broken down into separate uploads so using a lot of custom assets forces you to create a lot of small dependencies (for example) or circumvent the limit by having friends help you out with their filesize.
4) Map making is very time intensive and the editor while powerful is quite unwieldy. People often start out with a rough idea and then get lost in the editor or churn out a very early version and then stop.
5) Many map makers are rookies nowadays so they lack experience with the editor AND often lack experience in designing a good game.
6) We have a lot of custom assets now but the original game and scene at the start did not have as many and as diverse Warcraft 3 had to offer in the base game and we are a long shot from the Warcraft 3 custom scene at this point in time. Also see point 1 for early community disinterest.
Lastly the Starcraft 2 mapping community is now mostly active on Discord.