Lunar calendars are easier to track than solar ones. You can track a month by noting the day of a new moon, which is pretty easy to determine, and months are only 29-30 days. A lunar year is simply 12 of these. So it's pretty easy to keep track of time on a lunar year. To keep track of a solar year you are dealing with 365-366 days, and detecting solstices requires precise tracking of the position of the sun in the sky, which is not that difficult but is harder than simply looking at the moon.

The advantage of a solar year, though, is that it stays in sync with the seasons. Lunar years lose about 11 days every year, which means that they drift relative to the seasons. A solar year does not have this difficulty (assuming leap days are added appropriately; historically many solar calendars have tended to drift slightly)