I will let ACA answer for themselves but for me, a physical item can be resold as it is only one item and any royalty on a copyrighted item like a map has been paid with the original sale and only one person (OK, maybe a small group that shared it) can use it at one time.
A copied digital or photocopied map cheats the author out of what should be earned income because it is implied with the copyright you will not copy the product. This is exactly why all the songs, movies, etc. now require a special "reader" (website, Kindle, expires electronically, etc.) so you can't buy a digital copy and sell it so the author does not get their royalty. If you can't do this with songs, how is selling a GPX file any different? I should note that I think it is somewhat OK to copy/share it with an immediate family member, i.e. a husband and wife are doing the TA and they share the GPX file for their personal use.
Additionally, if selling the ACA GPX file would be legally permitted, what would prevent someone from just copying it directly and selling copies for $1 each? Granted, you could create an identical route on say RWGPS and then sell copies of it. Since you "created" that GPX file, that new GPX file legally yours though in my opinion not in the spirit that it was intended.
Again, I just see it as cheating ACA (or any other "artist") out of income they should get for creating the product. Plus I think it is tacky to sell the GPX on their own website from which you would be cheating them.
Finally, ACA is not some massive entertainment company that makes gazillions. I would suspect, they would very much appreciate the sell of that data to another person.
