It's more so because of demand, and Grants Pass is a little more than 12 minutes away.
I personally prefer seeing them at the Craterian Theater, not a bad seat in the house and great acoustics. It's also near some decent dining if you want to make a night of it. I've only been to a few performances at GPHS, but it didn't stick out as better. SOU is nice if you get good seats; it's an old venue and kinda cramped upfront.