Why does the Gregorian calender go the opposite direction from the astrological calender?

what you are calling the astrological calender is known as the precession of the equinox and has to do with where the pole is pointing (see these wiki articles)
[link to en.wikipedia.org]
[link to en.wikipedia.org]

vs the place in the sky where the sun raises during a given year. the sun comes up in front of leo in late july/early augst, and then in front of virgo during late august/early sept, etc.

Thank you