Because if you don't, the seasons and the months will drift out of sync with each other. And you don't even get the benefits of a lunar calendar as a tradeoff, because your weeks are shorter than 1/4 of a lunar month, and your months are two days longer than a lunar month.

> Because if you don't, the seasons and the months will drift out of sync with each other.

And?

> And you don't even get the benefits of a lunar calendar as a tradeoff

What are the benefits of a lunar calendar? And it's not like our 7-day week actually stays in sync with the moon, it's just approximately the same length.

> And?

People like predictability for planning things like travel, holidays, school, etc.

You can't just disappear them into the void. The length of a year is not something we can control.

We've changed the length of a year several times in history, what's one more?

The length of a year is determined by the earth's orbit around the sun. Sure, you can make a calendar that isn't actually a year long, and then correct the errors that accumulate every once in a while, either by inserting a few months every few hundred years, or by adding a leap day every 4 years, but why would you intentionally make a calendar that isn't a year long? Leap days are unavoidable, but seasons drifting out-of-sync are not.

We can define a year however we want, but then planet Earth will answer "Ok, then my new orbit is 0.95434 years".