Trying to make a legitimate mod pack is next to impossible. Mod authors may not be available, they may not respond (or if they do it's not in a timely manner), or they may not support the idea of their mod being in a package at all.

I don't know, the minecraft community seems to manage to do it in a way that doesn't disregard legal respect most of the time. Fairly sure the NEXUS could release a system to do it easily using the NMM, too. The biggest problem with ModDrop that I've seen is the fact that they're doing it illegally, and without any regard for the mod creators.

As far as your statement:

Mod pirates are filling in that service void.

This does not make something legal. Just because it benefits the minority does not make it legal. A drug dealer also fills a service void. I agree that people removing mods from distribution is less than ideal, and I would argue that they create a problem in themselves.

That doesn't make piracy the answer.