I may be wrong but I see that most of the accounts who want to gain rep in short time have one thing in common: serial upvoting of niches.
I experienced myself that ONLY upvoting niches got me at least one point in rep.
True or not true, this is what most users know. And this changes the niche approval process from "upvoting what makes sense" to "upvote anything" in the hope of gaining rep.
Upvoting niches may be part of the activity, but getting rep for upvoting anything doesn't seem to make sense, at least nowadays. And if it's not so, maybe it makes sense to be clear that it's not so, or to limit someway the upvoting. This now only leads to a multitude of niches that a few really cares about but that they upvote just in the hope (certainty?) of increasing rep.