I have an allergy to the glitz surrounding the idea that local events are always the key to trip planning.
Honestly, what changes tomorrow for the budget or logistics?
If your trip is motivated by professional obligations, like an important meeting, or personal imperatives, the fact that there is a Christmas market will not impact your plane ticket or your booked hotel.
It is rarely a decisive factor, unless it makes costs prohibitive or access impossible, like the Olympic Games which can inflate prices excessively.