The issue isn't universality but consistency. It doesn't matter to person A how person B gets their kids to school, what matters is that person A doesn't need a different system for half the year.
So everyone in the world changing their clocks is easier than having a summer schedule at a business where they open one hour earlier?
Many businesses have different schedules on the weekend, I think people could cope with summer hours. Especially since they already do - even with the time change many businesses are open longer.
For something so unpopular, how do places that don't do the time change get by? Why isn't Saskatchewan in a permanent rage-fueled civil war?