Those who intermix Valve maps with custom ones systematically attract people who specifically DON'T WANT custom maps, and then scare them off. Admins, there ARE people out there who want custom maps. Just be patient. If you build it, they will come. Perhaps people would be more willing to play custom maps if they knew what they were downloading.
People are lazy.
They don't want to download something that they're not sure they'll use. I was willing to get them in-game if they were good, and if a server was running one that I'd heard bad things about, I left. That helped a lot, but the community has grown a bit since then. Been there, done that, got the T-Shirt, burned it. I got some good reading done, too.