And they weren't surrendered to the US, they were surrendered to Egypt via the US.
They were surrendered to CIA agents at the request of the CIA. The CIA prefers to torture their victims outside the US.
It turned into one of the biggest judicial scandals in Swedish history, receiving widespread protest and condemnation.
And yet, despite being widely regarded as violating multiple laws, somehow nobody was actually convicted of anything. No functionaries, no officials, no politicians. So, yeah, violate the law and send people to get tortured and the newspapers will write a few articles about how bad you are and some will walk past you with a clenched fist in their pocket. Scary. That really wont happen again.
2) It led to a reform of not just Swedish but EU-wide extradition law, making it so that a mere promise of not torturing isn't enough, the country has to have a track record of not torturing.
And violating that will get you... a mean article in a newspaper and some angry glares?
3) The victims were offered by Sweden a large financial compensation package and Swedish residence.
Yeah, paid for by the tax payers. Oh, no, we'll have to give tax payer money to someone for violating their rights. We'll get cushy speaking appointments and nice educations for our kids in the US. But oh, no, tax payer money...
4) Swedish attitudes against the US rendition program
Most likely the Swedish security agencies got fed up with getting snickered at and played for total fools. I doubt it had much to do with ethics.
No country has a spotless record, but Sweden has among the highest ranked judicial systems on Earth.
... based on reported public perception. Swedes like to have a very high opinion of their country and government. They get very surprised when confronted with objective measures of education and discover how far they've fallen or discovering they get much better healthcare when on vacation out of the country. Filtering out self-satisfaction bias would be an interesting exercise.
Sweden has the world's best whistleblower protections and one of the most restrictive extradition treaties in Europe
Which means... what? If nobody is even prosecuted when torture protections are violated the law isn't worth the paper it's written on. Unless Thomas Bodström, Göran Persson and the responsible people in the security agencies are actually prosecuted and thrown in jail for what they did to the Ahmed Agiza and Muhammad al-Zery it doesn't matter what the law says, because they are above the law. With politicians and security agencies above the law, Sweden cannot be trusted to enforce the laws they claim to have.