On the surface, we like to say how we're providing care and have their best interests in mind as they "age well" and as we repay the debt of elders who took care of us so dutifully for years.
But in reality, the main usage is to get rid of very burdensome, cantankerous, and irresponsible leeches who because they left their children with a sense of hatred will not give in to the idea of putting up with their crap ever again, so let them rot all drugged up in a coma where they cannot escape as they watch TV in a urine-soaked room and play bingo every Wednesday night until they die off.
It's more a short-term fix for us though, a pretty typical American form of cutting off the nose to spite the face since national spending is sprialing out of control from dealing with the old and will become a larger economic problem. Ironically, it does force the hand of the young in later years once filial laws come back in full swing enforcement who will end up saying enough is enough and euthanasia legalization legislation will come swooping in to deal with this.