Potential payouts for 7 days are getting decreased my old posts. why this is happening? Could someone please explain me what's happening?

I know it's only a small amount but it's still valuable. I also don't know how it really works, I'm just kinda curious about it. The "potential payout" of two of my posts decreased by $0.02 and

So, I've been a member of the steem community for a couple of days now.  I must say, I enjoy the experience a lot.  I am a little confused still on how this works exactly.  I noticed that