My sense is that most events in the game equate to real-life happenings. Some are more obvious - Spirit's Eve = Halloween and Feast of the Winter Star ~ Christmas.
To me, the night market is equivalent to the kickoff to the holiday shopping season. It's like Black Friday weekend.
The other issue with adding events is that they usually cut off that map section and/or messes up the clock for that day (e.g. even if you stay for a short time, you exit at midnight). The night market is different in that it doesn't do these things. But because it seems to use a different map (crab pots/chests don't appear while night market is happening), it could still be an inconvenience for some.
If there was some way to incorporate added markets - either as night markets or at the community center or other locales - without disrupting the maps and clock, I'd be all for it.