Why do potential reviewers take a lot of time to reject the request for review? I understand that reviewers are quite busy and have not only a single paper to review. But, no matter how busy someone is, it should not take more than 2 minutes to reject a review request.

How did I get this question to my mind?

Well, it is a common question for everyone in academia, I guess. I am quite frustrated with the peer-review system and yes, I am impatient. Because after doing a lot of hard work on something and then achieving something real good out of this, which would lead to potential dissemination, turns out to be depressing.

We had submitted a work back in December 2016. Since February 2017, It was Under review. Suddenly, I see that it is Reviewer assigned. This system is really pathetic. Other parts of my question can be inferred from this.

As a reviewer, I don't reject the requests for review after 4 months. I would do the same within at most a week.
In addition to the Kerkyras answer, here is what happens all the time when I receive an invitation:


The potential reviewer needs to find the time to skim the paper to form a well founded decision to accept or decline to review.


I want to accept a review when I am sure that I have the expertise and time to do a good review. It takes about 2 minutes to decide if I have the time for a review (usually my conclusion is "no"), but to decide whether I have the expertise is more complex (and if the answer here is "yes", I often agree to review, even if the answer to the former question was "no"…). Hence, a basic skimming of the article is needed and this may take some more minutes. Some days (or even weeks) are extremely busy such that finding just 10 minutes to skim a paper is hard.