It's bad enough as it is in the northern latitudes where you wake up at about 5:15AM in June because the sun is already pretty bright. Keeping it on standard time would mean waking up at 4:15AM. Also, it's nice having more daylight after work.
In fact, in January, the sun rises here at 7:40 AM Standard Time. Which would be 8:40 AM Daylight Time.
It would be terrible to have to wake up an hour before sunrise.