Earlier quoted context omitted.
Perhaps it was easier in the times before the internet. Now a consistent timeline should be far more convenient than not having to change your habits by a little bit. Edit: If changing schedule is normalized, then it would be just as convenient as changing the clock. In countries without DST, if someone started using DST instead of changing their own schedule, it would be just as difficult.
Your argument sounds very similar to the "let's abolish timezones" argument so let me post this again: https://qntm.org/abolish Changing your schedule works for you and your boss, but does not let people in other parts of the world know when they can reach you. Officially shifting something is necessary, and then you might as well have timezones.
If Google today tells me, "It's now 5PM in Singapore", with no time zones it could just as easily tell me "Regular working hours in Singapore are 12-20".
OK, so that's two numbers to remember rather than one, but come on. Thing is, what a certain time means varies wildly country to country, and from person to person anyway. My Swedish friends eat dinner at 17:30. My friends in southern Europe eat dinner at ~22:00.
Unless I know who I'm calling, and their regular hours I have no idea if it's OK to give them a call at, say, 07:00 or 22:00. So I need extra information about them anyway - and that information wouldn't be harder to package in a world lacking time zones. In fact, it would be easier, since it'd contain only one element (times available) rather than two (times available plus timezone).