Recently I have observed that several users vote very low. Are there, peraphs, any specific reasons that can be made public?
I think we all have 40 votes, why not use them when there are good questions and good answers?
People vote or don't vote as they see fit, and it's really not for us to be concerned about how much anyone votes. Overall we're a vote-happy bunch, and we also have a tradition of not downvoting excessively.
But whether or not others vote is really not worth worrying about, at least on this site. Both questions and answers generally get enough votes to keep people engaged in the site, which is largely what the purpose of voting is (although it also can help users see the value of an answer).
Voting is anonymous, so by definition you should not know who voted or why.
You say you notice that some users have low vote scores, but how do you define low?
Vote count has little relevance to anything, my two highest scoring posts have essentially no technical content, and in fact almost no content at all, whereas some that took some days to answer only score one or two votes.
Personally I post far more answers than I vote as I think answering questions is a more useful activity than voting. (nearly 10 thousand answers, and rather less than 3 thousand votes)