Being Pro-Brexit has taken a fair few people down various RW rabbit holes. A good number of the people you would most associate with being Pro-Brexit happen to be on the right of politics and a person who is Pro-Brexit could quite conceivably have looked for evidence to back up their reasoning from various websites that unbeknown to them lead them down the rabbit holes. They become part of the Pro-Brexit team. Some of the leaders of the Pro-Brexit team know this and it gives them a captive audience to spread further propaganda. A person who starts out thinking Pro-Brexit is a reasonable political position is also subjected to what the Pro-Brexit leaders believe in, be it climate change denial, anti-vax, QAnon, etc They are also fed a diet of propaganda stating that being Pro-Brexit makes them a Patriot so they look to identify with other Patriots, that leads them to the MAGA stuff and the American Patriots. Hence on twitter you see a proliferation of flags . Human beings like to be part of a collective identity, me and you do it with City for example. That is part of our collective identity and as a result we will tend to see all things from very much a Blue perspective.
Good post Rasc. In summary then, it’s because all anti-vaccers are idiots and most idiots are pro-Brexit.