They spent hours and hours developing the yips because they missed putts and didn't know why. They kept changing things, trying to get better, and they changed the wrong things. The whole key to learning to putt better is learning what you are doing wrong and correcting it. The last thing is path, the direction of the stroke. The funny thing about that is that path is the one that's practiced the most.
Most people practice 'path' because they can see it, and that's usually the least of their problems.
They know in general where they want the ball to go, but they don't know in detail how to make it go there. So, they just kind of practice making it generally go there. They get their approximations and compensations, but they never get anything very grooved or accurate. I did a little survey on the PGA Tour. I asked 50 guys at what age they putted best.