You've completely missed the point here. It's not about being transactional but the general attitude.
My parents are like you and do things because they want to. Not because they expect care. They have made provision, but I will still help and not just leave them to it because we are a close, loving family.
Btw it's a very privileged, Western view to say that 'parents should make their own provision. In many countries there's no social safety net. Parents literally don't eat, giving food to their children and do backbreaking manual labour to buy them schoolbooks. No matter how bad it gets in the U.K I highly doubt that people are living in shacks with no electricity, and no school. If you think that after all that sacrifice the children who have made it good are morally right to leave their parents to 'make their own provision' when they didn't even manage to have a proper meal while raising children then you're a very callous human being. I'm lucky that my parents made good, but many others did not.
My husband's family however are the opposite. They have made it clear that they've got not time or care for us. The examples I gave were about money but there are so many other things that have made their feelings very clear. Their chief concern for our wedding for example wasn't our happiness, but how it would look to their social circle.
And unlike you, they don't think it's the 'job of parents' to look after their children they washed their hands of H once he finished A-levels. His parents were self-employed and not only took great care in making sure their reported income was low enough for H to get the full maintenance loan... so they didn't need to pay a penny. They also took great pleasure in bragging about it to anybody who would listen.
Now tell me - are we obnoxious to want to have very little to do with people who have made it clear that they want to have very little to do with us? Except when it suits them?
We're not monsters. No matter how cold and uncaring DH's parents are if they were genuinely in need we're not going to let them rot. Although technically, it's the job of the state to take care of them and we pay a lot of tax. We'd still step in.
But, as you said, it's not the job of children to look after their parents. So as they're perfectly capable of looking after themselves that's what we expect.
They love moaning about how DH never comes to visit even now but why would he?