How much do you want to depend on companies to do what is right for their workers? At least the government is elected partly by workers so they try not to totally overrun them.
It might suit the companies to get the workers at 10 am and that would slice the workers daylight free time into 2 useless portions instead of 1 decent length portion. AND that might suit companies. The "average" worker might tend to sleep until 9 am, get up and go to work. Then they can concentrate more on being "productive" because they will not have time to tire themselves out after work.
Sure, you could do that and mandate all government office workers to come in at 8 in the morning instead of 7 on some day in the spring. Some businesses would miss, some restaurants for instance and 50 people would go for food one day and nothing ready. It would be so peacemeal that it would be chaos. By changing the clock you avoid the peacemeal approach.
When I was in China, some companies had a revolutionary idea: their working hours would be pushed back an hour for so many months of the year. So their staff could still enjoy more sunlight without having to fiddle with the clock.
Now let's reverse the scenario. Imagine that here in Ontario which does have DST, a company decides that it would change its working hours twice a year to counterbalance DST (perfectly legal to the best of my knowledge). Clearly that would make us fiddle with clocks for nothing. So why not just leave the clocks and watches out of it and just come to work an hour later or earlier depending on the time of year? Same effect but without having to fiddle with all our clocks.