It's the liberal democracy part once again. Making airtight restrictions is illegal.Not at all; small businesses need not be 'sacrificed' by coronavirus restrictions, if they merely receive adequate support from the government. Governments have chosen not to provide that support.
Can't stop citizens from leaving the country either. You can look at mass spreading events and possibly point out how that particular person (who does their best to evade restrictions) could've been stopped with better screening and so on, but it only means there are risks actually everywhere but only some of them are realized. Most international travel worked just fine, even across the dreaded border with Russia. Until it didn't.Returning citizens and permanent residents made up a minuscule proportion of international traffic, even in early 2020. That level of international traffic could have been facilitated with mandatory screenings and proper testing/ tracing procedures. Instead, we had continuing international travel on a much larger scale, and non-functional testing/tracing.