LOL never heard of anyone refer to a bordering state as "down the street." As Osiris explains, even adjacent counties can be far apart politically and the huge differences you're referencing are in the vicinity of 20-30%. Not weird at all. Even deep blue California is somewhat bifurcated between coastal counties and moderate/conservative inland and rural counties.
You're also underestimating the reality of viral transmission, which doesn't stop at borders. Although I somewhat agree the anti-vaxxers put only themselves at high risk, that includes children who don't have a say, and the pandemic never ends with continued local, regional, and international transmission. Even if we miraculous vaccinated 90% of Americans by autumn, the end game doesn't appear to be so certain if most of the world slowly gets vaccinated, if at all.