It is selfish not to obey the rules, but as no police force has the manpower to go round handing out fines to people who are not following the rules, there is nothing we can do about it.
Here in Denmark, you would be asked to leave a shop if you were not wearing a mask, unless you had a doctor's chit stating that you couldn't wear one due to panic attacks, astma or the like.
The same applies across the border in Germany and no-one is disobeying the rule. A lot of people in both countries are wearing their masks in the streets as well.
I don't as I cannot stop my glasses fogging up - nothing works to prevent this, so I take my mask off in the street and pop my glasses on, then reverse the procedure before going into a shop.
The rule-breakers seem to be those who don't believe that Covid19 is dangerous. A lot of young and middle-aged people state blithely that it isn't more dangerous than an ordinary flu. They seem incapable of reading the daily statistics of deaths and new cases.
Presumably, when this is all over, governments will pass laws regarding behaviour under epidemics , so they can prosecute rule-breakers if we have other epidemics.