phrase usage - Why do we use "part of the reason" and not "one of the reasons"?

As the word reason is countable and one thing can have many reasons, I would imagine that saying "one of the reasons" is more logical than "part of the reason". However, many people (native and non-native speakers alike) tend to use the latter.

My questions are:

1- Is it correct to use "part of the reason"?

2- Is it correct to use "one of the reasons"?

3- If both are correct, is there any reason why "part of the reason" is more common?

Thanks

Answer

1- Is it correct to use "part of the reason"?

Yes, because saying it like this suggests that this reason is only part of a whole reason. If it were the whole reason we could say something like "the only reason..."

2- Is it correct to use "one of the reasons"?

Yes, because saying it like this suggests that this reason is only 1 of many reasons. If it were the only reason we could say something like "the 1 and only reason..."

3- If both are correct, is there any reason why "part of the reason" is more common?

I don't think "part of the reason" is more common, but perhaps it is for you. The beauty of the English language is its diversity in using it.