This has something mostly to do with the current price of Steem in the market. I'm not sure of the exact formula the blockchain has for one's upvote worth but one factor is the "3-day average price of Steem in the market".
The last 3 days have not been good for Steem as 2days go it even went down to $0.6. Less price = less upvote worth.
Well they vote a lot and this drains their voting power that's why done posts have up to a dollar upvote and some cents.
Again, they upvote you according to the relevancy of your answer when applied to the question asked and how intelligently it was constructed, more like what you give is what you get.
If you get cents, you should be grateful
In a way we get the same amount when voted. But since it isn't shown in Steem or Vests it seems to have gone down because the price of Steem went down.
I think we should abolish the $ and should show these numbers in another way, that would make everything easier.