If we just change so we do all of these things an hour earlier in summer we either have to change a whole bunch of signs and other printed material twice a year, or we just have to remember that we need to mentally take an hour off the printed time during that time of year.
The former would be a major hassle and possibly an expensive one, and the later would confuse a lot of people for days or weeks after the switches.
Clocks, on the other hand, are designed to be changed.
If we want things to start an hour earlier in summer, and we want that to apply to everything, than implementing that by moving the clocks an hour forward is easier, cheaper, and less confusing.
The main hassle with changing the clocks is that there are so many of the damn things, although I think we may be getting past that.
(I say this is the main hassle, rather than the hassle of dealing with biological rhythms getting messed up for a while around the time changes because this post is about how, if we are going to have DST, it should be implemented--change schedules or change clocks. The biology thing is the same under both, so is not relevant in this comment)
At one time, say before the 1970s, it wasn't much of an issue because we didn't actually have all that many clocks. A typical family might have wall clocks in the kitchen and living room, table top alarm clocks in the bedrooms, and watches.
It was in the '70s and '80s that clocks started appearing everywhere, and worse, no two seemed to have the same mechanism for setting them and the mechanisms were usually almost impossible to figure out without the instructions. DST changing could be a frustrating evening of alternating trying to guess how to set a clock and searching through every place you might have left the manual.
But now, although everything still has a clock whether it needs it or not, those clocks are more and more likely to be self-setting. I think I have 15 clocks in my house and garage right now, and only 3 of them did not handle this morning's return to PST from PDT automatically. (And all three are or are in old things that if bought today probably would automatically handle the time change).
I have certainly seen hours of operation signs with separate summer and other hours -- they generally also indicate when they think summer begins and ends. Even if you did change the hours twice a year, that allows you to adjust for changing demand as well -- you don't always need to keep doing what has always been done.
I personally don't think parking and lane restriction hours are that sensitive, just set them to cover the full range of high traffic times.
Most of your self setting equipment is likely not to adjust to changing dst dates when next we add more days to DST.
