Yes, you are right, I have seen a lot of quality posts on steemit with even thousands of upvote with low reward, the reason will be highlighted below.

Firstly, there is something we called steem power(SP) on steemit, the higher the steem power the higher the voting value just like law of Supply in Economics.

There are three categories of people on steemit according to their SP, we have whale, dolphins and minnows.

It could be from the percent those persons that upvote the post used, there was a time a whale do upvote all my post with 0.1%. For example, my voting power worth 2$ if I post with 100%, what will it be if I upvote with 1%? By doing simple arithmetic calculation, it will be 2/100 = $0.02, can you now see. That is the first reason.

The second reason is that if newbies are those one that upvote your post, no matter their numbers you can't see good amount on it. Using myself as a case study, my upvote value is $0.001 by voting with 100%, simply because of my low Steem power, I hope this answered your question.