If you're looking for an answer rather than a validated rant, I'll try my best.
It depends on what a persons main issue is, for them, in their mind. And what they're willing to compromise on to achieve that.
So for example, someone concerned with women's right to women only spaces, the protection of language and sports etc. may feel that this is so important to them that they are willing to accept a worse deal for certain vulnerable groups, and reluctantly vote with the party that reflects their views on gender. Likewise, those with strong ceasefire (read surrender to Hamas) views might feel that this outweighs the benefits of a Labour government.
Fundamentally, I think I agree with you (albeit I doubt if I'm quite as anti-Tory as you) if a person feels that a 100% of a party has got absolutely everything right and 100% reflect all of their opinions, they're either very indoctrinated and entrenched, or are a one person party where they are the founder and leader. In the end, voters generally should vote in accordance with what party is closest to their values and whos manifesto seems correct for the time. But there will be a fair chunk of people that will be so hung up on one issue, they'll ignore the wider picture.