That's what I'm saying, if they want as many people to learn Swift as possible, why not open source this learning software? The Swift language is open source under Apache 2.0, clearly the license is not alien to Apple.

I don't disagree with you, but your comment was worded in a way that implied you thought it was source-available.

Frankly, Apple probably doesn't care how many people learn Swift. Playgrounds is aimed at children, who don't yet care about software licensing.