Comment by immibis
Because someone said "we need security" and someone else said "what is security" and someone else said "SQL injection is security" and someone looked up SQL injections and saw the word "select" and "insert".
WAFs are always a bad idea (possible exception: in allow-but-audit mode). If you knew the vulnerabilities you'd protect against them in your application. If you don't know the vulnerabilities all you get is a fuzzy feeling that Someone Else is Taking Care of it, meanwhile the vulnerabilities are still there.
Maybe that's what companies pay for? The feeling?
WAFs can be a useful site of intervention during incidents or when high-severity vulns are first made public. It's not a replacement for fixing the vuln, that still has to happen, but it gives you a place to mitigate it that may be faster or simpler than deploying code changes.