Some of my writing is really personal or is loosely based in something real, I think a lot of people work through their own traumas or emotions creatively. I certainly do. It can help recontextualize something terrible as something you can now control. It can help you express something you never thought you could say out loud.
It could also be that, if it wasn't intentional, you've projected some part of yourself into that character or event. Maybe there's something in your personal life you've tried to ignore that really did hurt you, however unrelated, and it's coming up now because it feels more acceptable to cry for this character.
It doesn't have to be something massive, like grief or trauma, though it could be. It could be as simple as stress, and we're all stressed now more than ever.
Or maybe you just have a soft heart heh heh
sometimes it really not that deep. I've definitely cried over goddamn my little pony fanfiction and that's like as low as the bar can go.