Interesting questions and reactions to the use of a church for Christmas based activities. This can be for services and worship, which are a mixture of reflective and joyful, hopeful, in this season. However, there can be a lot more that is (for example) meeting need, that also goes on as it does in other seasons, such as food bank, drink or drug counselling, warm spaces, people in trouble or grief who need support. Not only does the winter often show these things to be really needed, perhaps more than the warmer months if anything, but the core of the Christmas story has all of this in there to ask that in your life you should aim to keep looking outward, be less hedonistic, careful of judgements, and show more love and hope, really. The general image of the festival is very family-centred and this can be great, but it can also be extra levels of painful for people who don't have that, or who have lost family.
The phrase: "wondering >why< you do (celebrate)" from the OP was interesting - made me think. I'm not always that joyful (that much might be obvious!) but I am hopeful and there are usually quite a lot of points through Advent when I am brought down to realise I (and the average person too) am/are vulnerable, and need hope, other people, less cynicism, etc. And also that I'm lucky. Even if there are years when I would rather rage at unfairness, or whatever. So it does get through to the heart.
Like others, the singing is what I would miss the most if I did not have that opportunity. I may not, always - as I get older my voice is not what it was, so even that might have to join the 'vulnerability and only human' reminder.
I've worked in some multicultural places and have had nice, though not OTT, staff lunches (perfect) where we just have a good time together. I really like hearing about how other colleagues following other faiths do things like carol singing or equivalent, and celebrations such as Ramadan and Eid and the things that I've found out from these. I love the different varieties of dates connected to Eid, that some colleagues didn't like so much! Definitely feel like a treat.
We have a Christmas tree, do other fun outings if we can, although the time for them is squeezed in favour of work, it's true.