It's a little like most hobbies really.
A lot of people really dig driving and watching NASCAR, but they don't build their own cars.
A lot of people like watching football with friends, but don't memorise player statistics.
A lot of people like watching television shows, but they don't read the production notes or scripting process.
Just like the above, a lot of people play D&D, but they don't build characters between games or worry about optimisation or plan their character ahead. There's a lot of casual D&D players, a lot of people thinking about the story first and character concept rather than build.
It's not that we're playing D&D wrong, it's that we are not the norm. We are not the baseline. We are the outliers and exceptions.