The main reason to do this is cost. Uls as we call them in Germany are significantly cheaper to operate. Until recently they were limited by a MTOW of 475kg which made their utility problematic. Since the weight limit has been increased to 600kg, as two seaters they leave little to be desired.
I got an instructor rating as soon as my club got one of the higher MTOW aircraft and am now the CFI. Previously I would have discouraged people interested in progressing on to higher licenses from going down the UL route. But now at least here in Germany starting with ULs and moving on to a PPL and beyond seems quite possible.