Most likely because you have the option to omit the time, and in that case, the argument will be a part of the reason, e.g.:
Code:
sm_gag #1 0 "you got permanent gag!"
sm_gag #1 123 "you got gag for 123 minutes!"
sm_gag #1 "you got permanent gag!"
First one demonstrates the first two here, and the last one demonstrate the last.