At my local store this game is one of the up and comers. We've built a healthy player group quite quickly from an initial core group of 3 people. The game looks great on the table. The characters are familiar to everyone and draw attention and bring out stories. The game is an attention magnet.
I think the lack of marketing is due to it being made by a small european company. They just recently got their US distribution running smoothly. They dont seem to have an official English speaking representative or marketing person.
Price. The minis cost a little more than Guild Ball minis, the other game I play. You can get much cheaper minis but then you are usually sacrificing sculpt quality/beauty. Also this is Marvel. If these characters are meaningful to you then I'm sure you're gonna get the few extra dollars in value from the joy of just looking at them on your shelf. I do. My Dark Avengers are looking at me from the top of my keyboard right now. They keep me in line.
Pinning. I have all of the avengers (good and bad), all of the guardians, and some of the xmen. I have pinned only Hulkbuster. They models have sufficient contact patches (if you sand/file them a bit) that with a quality glue they hold together very well. I am not precious with my models. I play with them a lot. I dont have a nice foam bag. My models get dropped and knocked over on the table. They are all still in great shape. To be fair I'm a miniatures noob. I dont have 10 year old minis. If mine eventually break I'll fix them or kick myself.
Community: There is a very active facebook group. Knight Models SuperHeroes Universe. Stop by and you'll find a vibrant and friendly community.
Heroclix. I think you cant really understand this games relative success without acknowledging heroclix. If you just want to play with your favorite superheros you can buy clix. It has much more market penetration. It can be much easier to find players. Clix is dead at my store though. The population at my flgs is mostly people who LOVE their minis. They want them to be beautiful. Clix aint that. Even with the Marvel appeal I dont think this game will be a mass market hit. Its still a build and paint miniatures game.