It is not implausible to imagine a scenario when Bob does all the same things and learns French, German and then fails on e.g. Spanish. The same thing for Sally.

A valid point.

If you have invented e.g. a new machine learning method to solve a specific practical problem, the obvious next step is to try to apply it to other problems.

There's a crucial difference here. Your machine learning method does not get tired, or bored. It does not say "to hell with this, I've had enough".

The stories point out the difference between having a successful method to do something, and having motivation to do it.