Among the reasons I have been given (none of which I agree with):
1. Too difficult/expensive/time consuming.
2. Coaches would be even more mad about results if they knew the true reason they lost.
3. Large gyms would be given an even bigger advantage than they already have.
4. Don't want to expose the judges to more criticism.
5. Losing teams would be embarrassed by their scores.
I personally believe that the primary reason is the fear of exposing mistakes. The top tier of judges are excellent & highly knowledgeable, but there is pretty significant drop off after that, IMO. Coming up with numerous panels that are all qualified and unbiased is an extremely tall order for EPs.
I also believe that the majority of arithmetic & "out of theoretical range" mistakes go unnoticed or unreported. Few coaches actually go through and double check the math when you eventually get the scoresheets back. We have seen enough mistakes to know to ALWAYS check them, but sometimes you simply don't have time to do that at an event. If the scores were public, these would get noticed almost immediately in most cases.