I think it's partly that. But as you say, they are not alike. There's no religious right here. Our church of England is socialist, if anything, but no one cares what they say about politics. There are some libertarians in the Conservative Party, but not a majority. We have no Trump (and Boris was nothing like him).
And it's partly the Irish hostility thing. Hating the English is a part of Ireland's identity. It gets very old. And it is still a thing in parts of the Democratic Party. As if the IRA was all about freedom fighters and not about blowing innocent people to smithereens.
And it's partly the pro-EU thing in the US, where the Dems think the solution to European problems is to be more like America! And then Britain does Brexit. But that's because Europe is not like America and we British value our sovereignty and flexibility. I wish Biden would respect our freedoms and our democratic vote to leave. It was a rational decision with costs and benefits. And it was not motivated by hatred of immigrants, as we sometimes hear, except in overwhelming numbers that we cannot absorb.