I can't speak for others, but I know I do this when I I am not positive that the answer I give will yield a result. Basically whenever I am suggesting steps to attempt to solve the solution. Sometimes those steps resolve the problem, and thus, I've provided an answer in a comment.
The question you link to is rather unclear actually: is the user not finding Activity Monitor (as the first sentence implied) or are they looking for ways to solve the actual problem of the computer running hot? So it's kind of understandable that people use the comment section to get basic issues out of the way and then focus on the actual problem in the answer.
In other words: Answers in the comment section are a good indicator that the question needs to be improved by editing.
I made my suggestion in the comments and also included a link to an Apple support page because I wasn't sure what the OP's actual problem was. I was trying to help the OP learn where to find resources to answer their questions (the unedited question stated they were new to Mac).
Should I have asked more probing questions to get a better handle on the question? Maybe I should've done that and it's a good learning point for me.