How do you expect stores to coordinate? If they worked during work hours, what's the point? People work during work hours, they don't go to stores. To solve this stores work around the clock or until 21 hour.
I don't. That's the whole point. Many/most stores, schools, companies, etc. are open about the same hours year-round. To the degree that people prefer those hours shifted relative to the sun at different times of the year, using DST provides that coordination at the cost of everyone having to change their clocks (or having a computer do it for them) twice a year.