I have started asking this, since I have not heard it asked in awhile (like almost 2 decades), and it is interesting to hear the responses.

It's clichéd question, but in my opinion it's a very good one and would still be useful if it wasn't so overused. The reason why is because there's one big reason why manhole covers are round and maybe 3-4 subsidiary and less important reasons why. A person who can 1/ identify that there's more than one reason, name them all and 2/ sort and rank the reasons correctly in order of importance reveals a person's clarity of thought and reasoning process.

My initial intent, because I thought it was so clichéd, was just to get a laugh.

But, I would say the majority had not heard the question before.

This is a younger cohort.

> Why is a manhole cover round?

Easy, manholes covers are round for the same reason JavaScript is the most popular language.

Answer: once round manholes became ubiquitous it became extremely difficult to make anything other than round manholes covers.