Not just holidays. I read books to my son. The other day I was reading him The Brother's Grimm's "One Eye, Two Eyes, Three Eyes". I usually read it to him with vocal characterizations, and I got all choked up. He asked me if I was upset because Two Eyes was being treated awful, and he said it was a very bad thing, and then he hugged me and said it would be okay, which made me cry even more.
We watched "The Forbidden Kingdom", and I got choked up and teary eyed at that as well.
Sometimes it's just a situation that makes us feel more deeply than other times, be it holidays, movies, or a good book. For me anyway, it's cathartic, being able to release these emotions in an expressive manner. Holding emotions in, even good ones, can overwhelm a person after a while.
Sometimes I think we hold in all these strong emotions all year, and then during the holidays where we are remembering good will and giving thanks, it all flows out of us in waves, cascading us in a flood of feeling.
Just my 2 cp.