Physics tells us that CICO predicts weight gain and heaps of empirical data tells us it's one of many relevant factors.
Most people don't really control their weight by counting calories. They go by how they feel and our feelings,are heavily influenced by our biochemistry. Semaglutide doesn't work by giving people will power or self control; it works by targeting GLP-1 receptors to make them feel full sooner.
Weight is a pretty poor predictor of planning and effort.
The overwhelming evidence is that for some people it takes far more work to maintain a healthy weight than it does for others.