Hello @ladybug4joints, Welcome to Connect. It sounds like you are doing all the right things to help with Osteoarthritis. I have degenerative arthritis and osteopenia which wasn't on my radar for taking any actions to improve my health until the past few years. The CDC has some info on the risks that might give you a partial answer as to the why.

"What are the risk factors for OA?
Joint injury or overuse—Injury or overuse, such as knee bending and repetitive stress on a joint, can damage a joint and increase the risk of OA in that joint.
Age—The risk of developing OA increases with age.
Gender—Women are more likely to develop OA than men, especially after age 50.
Obesity—Extra weight puts more stress on joints, particularly weight-bearing joints like the hips and knees. This stress increases the risk of OA in that joint. Obesity may also have metabolic effects that increase the risk of OA.
Genetics—People who have family members with OA are more likely to develop OA. People who have hand OA are more likely to develop knee OA.
Race— Some Asian populations have lower risk for OA."
-- Osteoarthritis (OA): https://www.cdc.gov/arthritis/basics/osteoarthritis.htm