Welcome to getting old!
I doubt this has anything to do with your bariatric surgery. Declining appetite as we get older is really common. in fact it's so common, they coined a term for it called the anorexia of aging. Obviously being really sick can drastically reduce appetite, but even in otherwise healthy people, there are multiple things that lead to appetite reduction. Common things are slowed gastric emptying, hormonal changes and impaired sense of smell and taste. Certain medications can also reduce appetite and since older folks are a lot more likely to be taking these meds, that can also contribute.