This is another chicken and egg type of dilemma... For people to post more comments, they want at least some rewards. Without upvotes they get no rewards from their comments (or posts).

I remember when I joined Hive and I got only about 3 HP from the fork and couldn't get much rewards from commenting... I ended up using about 40 EUR worth of ETH to buy HIVE and then powering it up... It didn't take long until I had enough influence that I didn't need to make any posts and just upvoting was enough to get my invested money back.

I still comment on interesting posts when I have spare time, and once in a while even make a post even if no-one reads and upvotes them.