which offers a degree
No it doesn't, it offers a "foundation degree", which is academically marginal, and of similar value to the old HNC. In fact I think I'd rate PPJD's HNC in mechanical engineering more highly, academically, than a BSc in "pilot practice".
A degree can also be a back up career if your career as a pilot doesn't work out straight away, or at all.
Generally speaking, this is also untrue. Most degrees are just a stepping stone to gaining significant additional experience towards, maybe, eventually, a professional qualification. Also if you do a degree, and then a few years flying training - the bottom drops out of the flying job market again - you're competing for trainee positions against people who have just graduated and whose study skills and degree education are 2 years fresher.
I really believe the Pro Pilot studies degree is a a degree invented by universities to satisfy demand by students
Yes. Airlines want pilots: a few third world countries like the USA think that a degree matters, but don't care what in - but in Europe certainly nobody cares and want to know how good a pilot you are.
The situation tends to be like this - young man or woman wants to be a pilot, but needs a loan as they're too impatient to earn as they train slowly. Parents, who come from another era when degrees had very different significance, want their child to have a degree. So, the solution is a "pilot studies degree", that frees up loan money, child gets to fly, parents see a degree happening.
I was part of the team that puts one such together - but we went for the full RAeS accredited Aero-Eng degree, and embedded a PPL in it. I think that around two thirds of our graduates went to engineering careers, and about a third to professional flying training. But the concept of "backup" was not there and we didn't encourage it - they were getting a broad education, and heading to the career they wanted. I was quite open with those who had no interest in an engineering career however, that they were wasting my time and their money and should just clear off and get on a professional flying course. Most of them ignored me until after they'd graduated.