Except doctors. Doctors refuse life extending treatments at a much higher rate than general population of patients.
Find a 4-5 story parking garage and stand up on the edge. That part of your brain that kicks in and tells you to get back down to safety will also tell you to pour every cent you have in to buying a few more weeks.
This can change when there is no "back to normal" available. When your quality of life is shot and you know that tomorrow won't be better than today.
In a suicidal person who jumps off that building we consider this a tragedy because there's usually no physical reason that those feelings couldn't have passed, why their life couldn't have been normal again.
But in someone with a terminal condition and a body that's just done... and especially if they're well informed about the realities of their medical condition... yes, there can be things you care about more than throwing every cent you have into extending the pain.
But I think there's truth to both points, and every single case will be different.
I believe the only blocker to allowing euthanasia in the developed world is a potential for abuse.
Part of this could be that pets are limited in their ability to communicate details of their feelings to humans, making it harder for humans to tell the difference between a pet that is acting off because of something that they will recover from without a trip to the vet and one that is acting that way because of something that is serious and is going to go downhill fast if you don't take them to a vet soon.
This leads to vets first going to the vet for a given illness later into that illness than a human with a similar illness would have went to the doctor, hence a greater chance of it being too late.
With my cat (and this would likely be the case with any of my cats...) we took a reasoned look at the medical options and the quality of life choices. It wasn’t exactly cheap, but we basically bought him a year of life. If it had been a human family member, we would have gone through exactly the same decision, IE: do you want to keep fighting and do you want to go through this procedure or not?
I suspect there is an order of magnitude in the difference in level of care that goes into the average person vs dog. I mean, for one, it is very common to hear things like - "well, you have to remember, their lifespan is short. They only have a year or so left to live." This just isn't a discussion that is had with people.