I will echo what has been mentioned above. I had to bite the bullet and take General Biology 1 and 2 last fall in order to check off some boxes for my applications this cycle. It was frustrating at the time, but I took them online and had them both completed in 10 weeks. Now, I know not all schools accept online labs or sciences in general so you have to look into that aspect, but it took the sting out of needing to complete those classes in a traditional 16 weeks per class scenario. I will say, having a bachelor of science already and (at the time) nearly 200 credit hours of transcripts with some upper level BIO, and as you said being a more "mature" student, that I learned quite a bit in those classes. Plus, if its 2 more A's you're adding in there, even better for your GPA!
To answer your question about why its a requirement, I do not have much insight into it besides the fact that the extreme competitiveness of getting into these programs has admission committees working to come up with what they feel will get them the type of applicants they desire applying to their programs.
I start PA school this January, and although GEN BIO 1 and 2 were not pre-reqs for the particular program I was accepted to, adding those credits and the A's that came with them did nothing but improve my application. Eye on the prize.