Is it normal for my ballet flats to get extremely slippery all of a sudden?

My black ballet flats have really soft, totally flat and smooth rubber soles that have always had really good grip. Lately though, if I have been in the kitchen doing stuff, I can feel them sliding on the tiles. It is the same when I am out, on some wet indoor stairs, where the rubber would usually be able to grip. It is also becoming difficult to walk notably in mcdonalds, public bathrooms even worse, terrible on wet grass, I almost got stuck on a little slope.
Is it something that is expected with shoes like this? Why before they had so much more traction?