Well, which standard do you use, and how do you ensure that your internal clock remains synchronized to that standard? For example, when starting your system, how do you determine the correct initial value for your clock, and how do you compensate for clock drift? Just having some monotonically increasing counter starting at some arbitrary value isn’t enough.

The current answer is everyone uses UTC, and they keep synchronized by observing the one universally disseminated time, which is UTC.