Can someone help me understand the credentialing process?

I am a provider currently stuck in the process of “credentialing” for a job I was offered (and accepted) last February. I admit that I am extremely frustrated with this process, but I am trying to understand it. From my perspective, I just can’t understand why this process takes so long. To me, logically it does not make sense. I have a completely clear federal as well as state back ground checks. My resume and employment history are very clear. (I am a relavtively new provider, so the work history part is pretty simple.) I have passed muster with three state licensing boards, hold a national certification, and two DEA numbers. Every one of those credentials required extensive checks and verification. If a provider has already passed board exams, gained board licensure, passed DEA checks and has a clear criminal and civil background check, what else do insurance companies want to verify? Again, logically: you can’t get a state license without undergoing a verification process of your education, work history, etc. You can’t get a national certification without them verifying the same thing. You can’t get a DEA number without undergoing an extensive background check, educational/license verification. So, then, why would an insurance company repeat all of this? It seems very redundant and unnecessary to me. I am not trying to fight the system, I am only trying to understand it at this point. Can anyone explain what I’m missing here? Why does this process even exist? Why does it take so long when so much has already been verified multiple times? I would truly appreciate any insight anyone has. Thanks for reading.