Simple? What if they think the entire range to care about are “my conservative grandfather” and “my liberal in-laws”? In other words this isn’t a litmus test unless the person even knows what the spectrum is.
Which is the point at which you return to Orthodoxy Privilege, or rather Ideology as people other than Paul “Not Invented Here” Graham has been calling it for over a century.
And yes, probably it’s not an activity most people engage in.
And the other problem is that those "unrelated" views on both sides of the spectrum are actually way more related than people assume and those common threads define the group so it's not at all surprising that you can see a theme and make predictions based on it.
An easy one for liberals, asymmetric power dynamics are bad. You can follow this theme to lgbt rights, blm, general anti-corporation, defund the police, drug decriminalization, generally anti-prison, supporting Ukraine, supporting Palestine against Israel, but also supporting Jewish populations at home, reducing the size of the American military, strong labor laws, unions, immigration, defunding ICE, civil rights, anti-insurance/single-payer healthcare, breaking up monopolies, taxing billionaires they all stem from this. You show me a sympathetic underdog and I'll tell you who the liberals will support lol.