I agree with the sentiment about spending thousands to keep an animal going for the sake of what? Sometimes not even spending thousands even, just invasive treatment that reduces quality of life as much if not more than the actual issue.
Yes the technology and medicine may exist but that doesn't make it the right thing to do. As said, quite often the treatment is awful and reduces quality of life itself, along with the illness or injury.
I have just faced a similar situation, I could have absolutely kept the animal going, but they were miserable with the treatment needed, it was a battle, but also with the management needed for recovery and to try and prevent it again, because we'd faced this before and each time the treatment got longer as did the level of management that affected quality of life.
I made the decision to not put them through it, I feel that there's far worse things for an animal than being peacefully euthanised with a kind word and pet to the last, and it's got nothing to do with money or lack of insurance.
It would have been for me I kept him going, not him, and I do think that's part of the issue, and that there's a belief that as long as the animal is alive then, to put it bluntly, it's better than being dead. I don't think some people can understand that's not necessarily true, I guess though that's just my opinion.