Like a couple of others, I don't care for the '68 Mustang/pickup, but the '66 isn't too bad. I've never seen that concept before, but I have seen a stationwagon based on a 1st gen Mustang.
I'll bet there were many discussions and meetings about the name. I believe there's a time-factor in keeping the rights to a name and maybe "Maverick" was getting close to that time where other auto companies could use the name. Hence the occasional "Cobra" or "Mach I" product.
As far as why...