I think it's the ages of my children - 9 and 11. A couple of years ago they were happy going for walks, on scooters, going to the park for picnics. Now they don't want to leave the house if we're home and just want screens.
I find it so depressing. If I could I would take them away throughout all the school holidays (I am already dreading the summer). Something just transforms us all when we're in a different place, even if it's nowhere fancy. We just live differently, eat different foods, are more keen to get out and about, can live a more outdoor life (if it's somewhere warm), are just more excited for life. It's just not the same at home. It's rained most of the week and there isn't anything exciting enough to leave the house for.