Changing the length of a second would be so insanely difficult that it's probably isn't worth attempting. Pretty mush every other standard unit has the second in there somewhere at some point, so changing that would mean spending decades of changing math on so many things. That story about the Mars probe that slammed into the planet because someone screwed up the units? That would be happening everywhere all the time.

In the end you're always going to have weirdness with time because the orbit of the Earth around the sun isn't going to be divided evenly by the rotation of the Earth. Whatever you do is going to come out janky, so why spend all the time and effort to change from our current jankiness to a different janky system? We'd have to put a lot of time and effort into solving the new problems caused by the new jankiness. Then someone else will probably propose some new janky system to replace that system, and it's a never ending frustration because we'll never have a perfect system because ultimately orbital mechanics don't divide into even numbers.

0 as the freezing point of water isn't arbitrary though, and neither is boiling.

They're both very useful reference points since water is universally available and you can easily tell when it freezes and boils, it makes it comparatively trivial and accessible to create your own thermometer which is likely to at least generally agree with someone else's.

this is the one aspect where i kind of prefer imperial measurements for distance, basing measurements on the human body means everyone has easy access to a reference that is likely to be not too tremendously wrong.

Obviously not super relevant these days, but back in the day it was a pretty neat feature. Like fuck, it wasn't that long ago that the meter and the kilogram were still defined by a SINGLE specific object kept in a climate controlled vault.