The phrase "a reason for not" is correct and can be used in written English.
You can use it when you are providing reasons why something should not be done. For example, "I gave him a reason for not buying the car."
This isn't a reason for not going to art galleries.
This is not a reason for not taking Saddam out.
"People are looking for a reason for not looking".
In my judgment, the Court has yet to articulate a reason for not deciding this case.
He had a reason for not paying any attention to any wrong results.
Is there a reason for not receiving regular, biweekly paychecks as a fellowship recipient?
If he can think of a reason for not writing he will".
The school cited a number of disciplinary episodes as a reason for not extending the contract.
Following price as a reason for not buying an E.V. is vehicle size.
Most recently, he has cited Internal Revenue Service audits as a reason for not releasing them.
I've never heard a referee give that as a reason for not giving a penalty before.
