Why do prior sevice personnel get treated like they are AIT recruits when they process back in?

I have three MOS's. I first started out as a Medic and in my course, there were a few prior service, one Infantry guy (he was a SGT) and a SGT that was AF. 232nd Med BN does not care about prior service. All Soldiers were treated equally like dirt. When I went thru my 2nd MOS of Engineer, prior service status was much better. I, and the other 4 prior service, were sent down the hall of the barracks to our own little area. We were allowed to leave in the evening to go where ever we wanted as long as we reported out and back in. When I went thru my 3rd MOS of Preventive Medicine, it was the same thing as the Engineer part, except I was in completely different barracks. So, to answer your question, it all depends on the unit you train in and the personnel in that unit.

I remember when i went to basic. We had 3 priors. One af one marine and one navy corpsman. They all got e-5 had separate barracks, there phones, went to the px everyday ect. Was accualy cool the marine would make a list of what we wanted and go get it. But bothered alot of us that they got treated so special but were going through the same trainning.

That does not always happen SPC (Join to see). I was prior service in 1976 when I was a new cadet at West Point which included getting treated like a brand new cadet at times.
Later I commanded an infantry training company where we had soldiers ranging from 17 years old who were taking part in split cycle training to 30 year olds who were a mix of prior service or other military service. Physical training and basic skills training needed to be gone through by all IET soldiers.
I knew of some soldiers who came back in with a few months of leaving service who did not need to go through the BCT phase - that was in the 1980's I don't know what the current rules are; but< i expect there is still a time limit between leaving the service and coming back in where you can skip part of the initial training or perhaps all of it if you are returning to an MOS you held before.