Because their opponents hold views? That’s stupid, potentially suicidal, an even more potentially putting all sorts of people in harm’s way. Sometimes the people back in the days where polio and TB were problematic had more sense in their heads than our government has now. Even NASA quarrantined Apollo Astronauts as a precaution against space germs.
There were some people who, either through religious conviction or political suspicion, resisted the vaccine or inoculations but the matter didn’t capture either Republicans or Democrats. Today everything is toxically politicized so that the reasonable ban on air travel is seen by some as racism and worse.