I don't think you've considered the ramifications of switch to UTC..
Take for example a company with offices across three time zones. "Our office hours are 9-5" would become "our office hours are 9-5, 10-6, 11-7 between these dates and 10-6, 11-7, 12-8 the rest of the time".
Then, consider the shift in operating hours of most establishments in the spring and fall. Even if you officially abolish time zones, they're still going to persist unofficially because the chaos that would be caused by leaving it up to each establishment to decide if and when to shift their hours is just too great.
They are still very useful.