How, specifically, does this explain their opposition to masking and vaccination?
They don't trust government policy makers are telling the truth about the effectiveness of masks and vaccinations--the same reason many democratic block voters like African Americans have low mask and vaccination usage rates.
Part of that is caused by stupid conspiracy theories and scientific illiteracy, but partially because its pretty obvious the government does lie to use when they think its for our own good.
Though part of it is valuing individual liberty over a slight reduction in risk of death. They are more willing to value sending kids back to school even if it means some 80 years olds die a few years earlier.
The right smears the left with similar accusations. Every time an illegal immigrants rapes/murders/etc. you'll see them accusing liberals of the same thing--not caring about children's lives, etc.