I don't personally find achievements motivating, but a lot of people do. That same mechanism can be a powerful force for motivating people to learn and gain mastery over software that they might never otherwise have gained.

I'm occasionally frustrated that I don't know how to do lots of things in Photoshop and Illustrator, for example, but don't have enough incentive to learn how to do them. While I don't think achievements would work for me, there are undoubtedly many people in a similar situation for many kinds of software that it would work for.