Yes, it's arbitrary, but we're on a continuum somewhere between every couple feet the time changes a few minutes and no adjustment at all and it feels to me like we're close to a happy medium.
I mean, when someone schedules an across-timezones meeting they use software anyway; and who really cares about that one time 2 decades ago when some small region switched timezones or whatever? (yes, I'm painfully aware that there are changes to timezones across the world pretty much every month; what I'm saying is how often does anyone really care about the historical changes, in contexts where the hour or 30 minutes really matters?)