It's down to hardfork 19 (HF19). It took power away from the power voters (who used to do their full 40 votes a day) and instead gave power to the minnows, while ensuring that voting power drains away after 10 votes.

They assumed that the minnows would replace the power voters - what has happened is that the minnows use their ten votes on themselves (posts and comments), and the power voters can only do ten votes a day instead of 40. So voting has collapsed.

As with all things just a few people were doing all the work to make this platform nice. Restraining them and expecting the masses to make up for it was folly.