Reason For Low R/T Availability?

The manager at the dealership I bought my Nitro R/T from said the reason for the low availability was because of difficulties with the supplier of the fenders. Not sure if it's true or not, but why then would the SLT be in better supply? Or isn't it? Note that I had already bought the R/T and was there to pick it up, so there was no reason to lie at that point.