The metaphorical person on the street can wrap their head around why having a gun in a person's hand gives that person power. Everyone basically knows that the gun control debate is a debate about who has and is allowed to have power.
I'm not sure the metaphorical person on the street even knows encryption exists; if they do, it's only very vague and probably an entirely incorrect understanding of it.
As for people who are for one and not the other, even though I'm personally in favor of both the second amendment and encryption in the hands of people, it's not hard to see a meaningful difference between them that would make it reasonable to have differing opinions. Guns in the hands of the populace is a positive power to do harm, encryption in the hands of the populace is strictly defensive. Criminals can use encryption to defend things we'd rather not have defended, but that is fundamentally a different concern that criminals using guns to attack things we'd rather not have attacked.
I think the only weird case would be being in favor of gun rights but thinking the government should have back door access to encryption, on the part of someone who deeply understands both. That is to say, I'm sure you can find people who believe both those things, but I suspect the latter is mostly an un-thought-out instinctive reaction to generally trust authority figures who seem generally trustworthy to them combined with a lot of ignorance about what encryption is and how it works. Humans have an all-but-instinctual understanding of physical weapons, encryption is basically magic by comparison.