copy pasta from /r/starcraft:
I think it's more about what they haven't done.
Out of date business model:
Look at any game that sc2 is currently competing with, CS:GO, Dota, LoL, F2P, yet you can buy things in that game, skins namely, this adds potential for not only more community involvement (workshop) etc, but also allows us to spend more money on the game, and allows for new players to play the game and get hooked.
Adding minor skins isn't a problem for gameplay, we've already seen this with the Zergling/Zealot/Marine/Overlord/Depot skins that you get as leveling 30 rewards. Add more minor skins, make them for every building and unit, and make them cost money, gg.
Gameplay Support:
More directly, they didn't support gameplay enough. Changes to things that were hurting sc2 as a game, and as a viewer esport have always taken way too long to fix, Broodlord/Infestor, Archon Toilet, Swarmhost, etc.
We all understand how drastic changes also drastically affect the meta, peoples livelyhood can depend on this game so taking small steps to make sure things don't change too rapidly is smart, but they take too long, and in the meantime the scene suffers.
Ladder issues:
This is an obvious one, since the game has died down in its player base there has been massive ladder problems, players stuck in the wrong league, going 50-2 and still not being promoted because of inaccurate distribution numbers, new players being put up against players with 200 games player, this demotivates both new players and veterans.
This has been going on for a long time, and we've only recently (last week) had an hotfix, which as of now has done practically nothing, falling back to the "taking too long" part of my last paragraph.
Maphacking:
Another obvious one, hacking has been running rampart for awhile now, it's hurting the game drastically, and Blizzard have been largely silent on the issue. We don't even know if our efforts to report these hackers has had any impact.
We need more transparency, give us updates, let us know what's happening, tell us how we can help.