I can definitely see the appeal of recumbent trike and would like to own one, but I definitely do think the traditional diamond frame has remained more popular because it's more practical and usable in day-to-day life. It's also cheaper to build.
My old Raleigh Pioneer lives at the bottom of the stairs in my apartment block where it's always ready for use. I couldn't store a recumbent there as there just isn't room. Not everyone has a garage.
With the wheels removed, any standard bike can be easily fitted into the back of my small Toyota. I'd imagine it would not be so easy to transport a recumbent.
Again, when touring, a standard bike can travel in the hold of a bus and I've taken bikes into my hotel room on plenty of occasions.
Shared use paths often contain width restrictions and other inconveniences which would be much easier to negotiate on a DF.