Sugar as a fungible and fiber-free isolated ingredient made dessert baking more economical and of course we love sugar naturally so demand skyrocketed. The Caribbean slave trade and the decades of indentured servitude that followed was really pushed by new high demand for sugars. Pies got sweeter and more decadent. People aren't today baking turtle or rabbit into their pies with a few dried apples for flavor. They're wrapping syrupy fruit in fat and flour -- or in some cases just making pies with sugar fluff alone.

Grandma herself is generations removed from the original rationale for pie and we're even more so. You're right, pie is a blight today despite being oh-so-nostalgic. You don't need to seek out something so obviously sickly sweet as grandma's cherry pie to find issue though. Pasta sauce, bread and even processed meat contain far more sugar than at any time in history. Fruits and vegetables are even sweeter due to our crop selection and our meat contains more fat per gram of protein because of our farming methodology.

Just by eating an ordinary American lunch today, we probably take in in something more nutritionally similar to our former generation's special weekly indulgence than their evening meal; literal pie is just the cherry on top.

Humanity has never eaten so much carbs + fats at the same time as we do now.

The fact that your dear grandma makes it does not make it less poisonus.

Even our grandparents eat totaly different foods nowadays then people 200 years ago do, so even though grandma is old compared to us, she is still a very young compared to human evolution and our dietary changes.