[jerf]

I hypothesize that it is because we can predict the astronomical days centuries in advance, which in particular means that we can print calendars with "start of $SEASON" days on them with no fear that weather or something will contradict them.

I live in Michigan, which has a highly unstable climate. In practice as it happens right now, we're really more in "late Fall" than what we'd usually call "winter". Other years, winter has come in early November. Only the astronomical events are predictable in advance.

I offer as evidence the fact that the primary place I encounter these dates is on calendars. And once they are there, I think we have very little left to be explained; trusting words that appear to source from an authority even over the direct personal experience of our own eyes is a very common problem.