That used to be more of a problem in the past. Nowadays, it's very common for a computer to have its clock synchronized via either NTP or a cell phone network.

Sure, it's common, but I work with devices all the time that have no access to the internet. Cameras, robots, and scientific instruments. Many, like the raspberry pi, can't even keep time when they are turned off. I also go on expeditions where I have no internet access for weeks. A time - based filesystem would be useless in all of these cases.