I am not aware of any EU regulations that would force a switch from tallow? If that was the case, MWF, D.R. Harris, Cyril R Salter, Phoenix and Beau and others would all have had to switch to vegan as well and remove tallow.
I do not think there are any specific regulations that are forcing the change from tallow to vegan in the EU. It just seems that vegan soaps have a greater following in the EU than in the States where tallow soaps still dominate.