Yes: when you couldn't feed yourself, they fed you; when you couldn't control your bowels, they cleaned you; when you couldn't control yourself and broke something, they didn't throw you out.
But if you were ever sick--really, really sick, not just with the sniffles but with something more serious--they would have taken you to the doctor or the hospital...and they would have done so, I'll wager, because they loved you. They would have recognized that you had a problem that was beyond their ability to handle--a problem that required the attention of an expert, someone who had the knowledge and training to make you well again. They would not have tried to save money by handling it themselves; their decision to put you in the hospital would have been a fulfillment, not an abdication, of their responsibilities as parents.
Though it's difficult to contemplate, your parents may one day end up in the same state--they may need more care than you know how to provide. It happened to my grandfather not so long ago as my grandmother's illnesses slowly grew more and more severe. He didn't want to put her in a nursing home for all the reasons that you describe; he'd been married for 60 years, he said, and would not simply put his wife away.
My grandfather is a man of incredible patience, strength, and charity, and he held out for a long time--longer than most people would have (and perhaps longer than I would have, though I'm sixty years younger than he is). But he's not a doctor; even if he were, he could not have provided adequate care by himself for 24 hours a day, which is what my grandmother ultimately required. Eventually, her condition degenerated so much that he was driving her to the hospital almost every day...and at that point, he agreed that it was time. He held off even then--he could not bring himself to put her in right around Christmas and their anniversary--but ultimately he realized the necessity.
Yes, some people may give up too easily, but--sad as it is--there may come a time when it's necessary. It appears that you love your parents deeply, and if so, you would not want to hurt them by withholding necessary care.