1. I don't want to have to spend time researching subreddits just to figure out what I'd like. Content aggregators are meant to remove steps from the process, not add them. 2. While the content of smaller subreddits are usually improved, the level of discourse in comments are not. Even if you say 'okay, no meme posts, no meme comments', the fact is that you're going to have a glut of commentors whose first impulse are to crack a joke or make a surface-level comment. The difference in comments between a post on here and a post on /TrueReddit/ are astounding.
(The one pretty ready example to the above are < 100 member subreddits, but those usually have the issue of insufficient content.)