My main point is that you've done nothing but kick the can down the road a little bit, so people decided it wasn't worth the trouble. It's annoying that there 60 seconds in a minute, 1800 in an hour, ~86k in a day, fair enough. Let's say you make a new metric second that has 100k in a day. You make certain things easier, but how are you keeping time on anything like a larger scale?

You can probably come up with something fairly usable with ten-day weeks, but what about years? This is is where it breaks down. A year is based on astronomical events, but different ones than a day, both are deeply ingrained into the routines of life. It is 365 and a a quarter (-ish) days in a year. We're stuck with that, unless you just want a number that has no useful context for humans after a few years. Throw in that you also have leap seconds to add every so often, and in the end it's still going to be a mess of decimal units that go unused, and customary units that will not be given up, but with all the drama of making a change.

There is no single bandaid to pull off, so it's not the obvious improvement that other weights and measures are, because time is more fundamentally rooted in our experience as animals than what we label a given amount of stuff.