It removes ambiguity between ET (which do I mean?), EST (oops I meant EDT), and EDT (oops I meant EST). I suspect they probably had an issue related to this, a

It removes ambiguity between ET (which do I mean?), EST (oops I meant EDT), and EDT (oops I meant EST). I suspect they probably had an issue related to this, and prevailing time seems to work for them. UTC is probably better, but a little less intuitive for most people.