Like, what exactly is your average, normal pro-life person who happens to also kinda support gun control and kinda oppose the death penalty and maybe even favor universal healthcare supposed to do, in the voting booth? Recall that their belief may be that abortion is equal to or at least very close to baby murder, before answering. Their options come down to voting for a 3rd party that's pro-life but agrees with them on some other positions, which is so close to not voting that they may as well be identical and anyway I'm not sure such a party exists (usually they're more extreme, if anything), voting anti-baby-murder but also against all their other positions, or voting pro-baby-murder but for the other things they like. This is clearly not a great position to be in.

So rather than going around feeling shitty about their own politics all the time, they soften or reverse their opposition to bundled views they wouldn't otherwise agree with.

[EDIT] this was highly visible in the last Presidential election, when a lot of the "WTF happened?" interviews afterward went like "yeah, of course Trump seems like a slimy piece of crap, obviously, I mean have you listened to the guy talk and have we all forgotten how he was, not that long ago, the universal media symbol for highly-successful rich scam artists? But I prayed on it and in the end held my nose and voted for him, because judicial appointments and Roe v. Wade".