Disco was the up and coming style during that time, reaching an on par balance with Hard Rock. Think of Olivia’s hit song titled “Let’s Get Physical”, inspired by the Jane Fonda Fitness tapes.
The Theme song may have been an attempt to catch the ear of the kids too young to know anything about music from the 1950’s.
A marketing choice to broaden the appeal.
I know, you're probably right, but still, it was weird to me. Sign of those times, I guess, thank god those days are gone.