But they'll let people in who have long term residency permits, or to visit long term partners, sick family members, or e.g. if their young children live there.
For Switzerland I know there's even a clause that lets you in if you have to go there for business. Kanye West was spotted in the country last month, I guess he was allowed in because he's building a villa there.
All countries have various levels of business travel, for example obviously all courier services and shipping still happens and other exceptions are made all the time depending on the situation. Diplomats can still travel. Kanye West can probably come up with a legitimate reason to travel to Switzerland even if he spends half his time on the ski slopes.
I'm always stunned when I see these questions because I am like "People are traveling internationally - test or no test????"