It's not just for the sake of sovereignty. The article clearly gives a reason why Finland might want to but other countries might not. Your individual reasons may not apply to someone across the continent just as someone's US east coast reason may not apply to Arizona. That type of thinking ("why not", "just for the sake of sovereignty", "here's my anecdote", etc) is what causes this type of federalist mis-representation so far from the problems of locals.
Some people are from one US state and live in another. Despite your anecdote being only yours and ignoring the wishes of entire countries, I don't think it's even a valid point to centralize DST above the country level.
What about:
- measurement systems (metric, ....)
- unicode
- electrical grid frequencies (50 Hz in all of EU)
- unified road driving rules (green/red lights, ...)
- the euro currency
- electrical wiring standards/colors
- paper sizes (A4, letter, ...)
You could argue the same thing for pretty much all standards.
Why not let each group of people pick it's own set of rules which perfectly suits them.
That is the point of standardization. It drives costs down, just like the invention of the shipping container massively improved transport efficiency.
Of course, and you can argue colors of the sky and everything else. Back to the subject at hand concerning DST, its value is affected by presence of daylight, and that is different for different people. Not sure why you are bringing up a bunch of non-daylight related items into the discussion for comparison. Maybe some standardized law about requiring air conditioning or some law mandating sunglasses at certain hours on the clock would be more apropos. Regardless, comparisons here do nothing but deviate from the DST discussion.
Obviously for some things commonality has value and for some things it doesn't, can't just say "let everyone choose everything then" as some form of counter or we cannot discuss productively.
But then again, being in Australia, and most business being done in the US, Europe and Asia, you’re not going to memorise all the time zones.
I'm from one EU country, live in another, I know that the delta between the two is always 2 hours.
Because EU and US switch DST at different times, in the multi-national software companies I worked there is this two week period when the delta changes, and there are mails and mis-scheduled things all around.
It's not a huge thing, but what is the benefit of each country randomly switching times, just for the sake of sovereignty. Next people will advocate using true solar time and getting rid of full hour based deltas.