I'm sorry, but even when you have very deep, highly acclaimed titles on the service there is still a major issue of developers hitting the threshold, even with lots of advertising muscle behind it. Nintendo simply doesn't care about the downloads aspect since it doesn't generate as much attention as their retail efforts.
The only way to get some really fantastic games out on WiiWare is if developers have enough of a big budget to work with something unique, and even then there are so many limitations, from size to what they can do on the hardware. And if the game manages to be too ambitious, there's the matter of money. Games cost money to make, and the better the game is, the more money is going to require. Nintendo doesn't really care for WiiWare. At times they will pretend like they do and eventually throw a bone here and there for SOME choice developers (the BIT.TRIP guys), but ignore the rest.
This means that the game, even with all its critical acclaim, still has to try and sell it to the audience, an audience that consists of casual gamers that have no idea how the Internet on the Wii works and another part of the audience that cares primarily for Nintendo's first party efforts. No advertisement, no support, no downloads.
You can say "but X game was popular!". Well, they got lucky. WiiWare had issues from the start, from memory being an issue to how Nintendo treated the games it received. The problem isn't the quality but the platform it is on.
Remember how we were supposed to get Super Meat Boy as a WiiWare exclusive, and the bigger it got the more limitations it experienced? That has been hailed as one of the best downloadable games ever, and it was supposed to be for WiiWare. But what happened? The system happened. So fanboys can claim that third party developers just needed to make "better games", but when the service is as clumsy as it is, you could make the Skyward Sword of WiiWare games and people wouldn't notice, and if they did it would be a very small number.