so why are the seven days of the week named after these planetary bodies?
No idea and don't care there are a bunch of other civilizations who named days and years based on moon and the sun. Just a honorary title because it sounds cool. Why did you name your account redExorcist and not Ronald Mcdonald? Why is a pointless question just person preference that is all.
Seconds, hours, days, months, years are nothing more than measurements of time what you call them is irrelevant.