Yes, I have noticed that too. There where even moments it did hurt a bit, working days on a painting and then the feeling it wasn't good enough. I took votes as curation and thus a measurement of value a bit too seriously after reading all kinds of blogs about growing naturally and quality becoming apparent. Silly me...
I have noticed different times of posting making a difference but I thought that was more about the time differences and the specific people who are interested. I don't track it either.
It probably is about the time zone differences. I'm sure it can help to be on here when majority of people are on. Don't let it get to you. It happens to all of us.
I think you are right