The names we have these days came to us via the Romans, July comes to us thanks to Julius Caesar and August thanks to Augustus Cesar. There was the Julian calendar etc. and a semblance of standardization only set in with the Gregorian calendar.

Since days, weeks, months etc. are measurements of time it is only natural for them to be named after the heavenly bodies and cycles by which we measure time.

Genesis one stipulates they were provided to mankind not only for light but also for "signs and for seasons"