reasons (for) as to why

Question

I just wrote the following sentence:

… there might have been interesting reasons for as to why they did.

My question concerns the passage "reasons for as to why". While this sounds perfectly right to my non-native speaker self, I wonder whether it includes just too man prepositions and whether "reasons as to why" would also do the trick. Any ideas about the difference between "reasons (for) as to why" and about which one ought to be preferred?

(By the way: google search provides hundreds of thousands example for both.)

Answer 1

__(By the way: google search provides hundreds of thousands example for both.)

Only because you're using vanilla Google, which is full of samples from uneducated or from non-native people. Use instead Google Books, which contains published books, many of the professionally edited. The results there are clear:

"reasons for as to why" 7 results

"reasons as to why" About 525,000 results

"For" should not be used when you have "as," or one risks sounding at best dialectal.

Answer 2

"… there might have been interesting reasons for as to why they did."

I am not sure what the ellipse at the start of the phrase relates to but I would personally not use the "as to why" phrase.

I would word it this way and finish the thought in this manner.

There might have been interesting reasons why they did it, but I could not imagine any of them.