why can’t i daydream properly anymore ?

I LOVE to daydream, always had since i’m a kid, imagining myself in some peaceful place of my favorite tv shows/movies with my favorite characters  etc.. like a lot of people yk. The thing is that i’ve always been able to imagine every scene very precisely, detailed, as i really was in there.. especially during class in highschool where i could do that for hours with no interruption. But since im in university (starting my 3rd year in september) I just can’t do it anymore. I don’t know why at all. I struggle to just think about a few seconds scene without being distracted or fully focused. I’m currently working in a factory, and I would love to do it when i’m bored but it just wouldn’t work.. I have no idea why, what are the reasons.. It makes me upset because it is such a safe place to me..