!nextmap preventing !votemap is a terrible way to stop !votemap spam for myriad reasons, mostly because the player count and roster can change meanwhile and because it (partially) fixes the symptoms of !votemap being bad instead of fixing !votemap itself.
If someone spams !votemap maliciously then report them. Any vote can be used for that so preventing !votemap won't help.
As said before, the endless !votemap spam is a result of the democratic room culture. I believe forcing people to use a random featured map would prevent that but would need all featured maps to be downloaded and the featured map pool to exist (as opposed to supported map pool).