MNN published this interesting article that looks at possible reasons that Americans overall are running marathons more slowly now than in the past.
https://www.mnn.com/health/fitness-well ... ing-slower
Ultimately, the answer is a mystery, but some theories are shot down and others are suggested. One possibility is increasing obesity. Another is that marathons have turned into parties and shopping events.
I often bike in and around Balboa Park in San Diego. It has some hard hills to enjoy. I have noticed that most people in the park are not active and a substantial majority are over weight, including the children. On Friday evening the City brings in food trucks to feed them. Crowds flock to this event. The food is greasy, sugary stuff. People drive to the park to eat the bad stuff and then leave after resting from their meal. Increasingly, people move around the park not by walking, but by riding in electric carts.
Balboa Park is where the Rock n Roll Marathon starts and ends.