Senior cats and euthanization...?

I've seen a lot of questions these days about senior cats getting ill and automatically, their owners probably without vet consult. decide it's time! Ex: if the cat stops eating or if the cat starts peeing everywhere or their cats start to hide..... some owners don't even bother to have a vet exam because they say their cat is old! Some say their cat goes in hiding because they know they are about to die. They don't realize the cat might be in pain and it might be just something simple which is treatable. Seems like people just want to get rid of senior cats. My senior cat is going to be 17 in November and I just adore him! Why are people so quick to have them euthanized or just want them to die "naturally" as they say without giving a **** if they suffer?!!!