It's more complex than that. People may need stimulation in order to follow through a certain learning process.
Providing a structured path and (automated) test means can be stimulating, and can make the difference between (deciding to) learning something or not.
Some people are certainly entirely autonomous, but at the very least, there is a spectrum of need for stimulation when approaching a topic of study.
AFAIK there are no other services that provide multiple languages, automated testing and team features, but if you know of any, it's certainly useful to report them in this thread.
Exercism is the closer service I can think of, but it's based on simple exercises, not real-world projects.
There are a few books that have a similar target (build X), but much narrower in scope (either a single language or pseudocode, and certainly no automated testing/team features).
Providing a structured path and (automated) test means can be stimulating, and can make the difference between (deciding to) learning something or not.
Some people are certainly entirely autonomous, but at the very least, there is a spectrum of need for stimulation when approaching a topic of study.