It isn't always true that most games happen at night. Many games, especially NFL games, occur in the middle of the day. Additionally, a 7pm start time on the east coast equates to a 4pm start time on the west coast, which means that an away game could land right at the peak of an afternoon commute. With that being said, it is very true that most listeners will finish their commute long before the game ends. I find it a little hard to believe that listeners will go through the trouble to stream the audio of a sports broadcast from home when watching it on TV/video streaming is available.
On the other side of the argument, I'm sure there were plenty of Mariners fans who preferred the voice of Dave Niehaus over the television broadcast.