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Short answer is Sticks and Stones is not dependent on the map while Capture the Flag is. Since we have a limited set of maps for CTF and do not have a great way to limit the map listing dependent of game mode, we’ve not enabled CTF for custom games just yet since attempting to load CTF on an unsupported map can cause issues.
Hope that explains the decision for you. I will check on the status of getting CTF added to custom games in the meantime, which means support on all maps.
What about Infected and Deathmatch Domination? Those seem like they would be much easier to implement, but still haven't seen those either.
You’re absolutely right and I will see about having those added for our next update. Thanks.