The sad thing is that Apple seemed more inviting to developers before they got high on the App Store cut.

Every boxed Mac OS X came with a second disc containing the SDK (Xcode has always been an unstable cow, tho). They used to publish tech notes that explained how the OS works, rather than WWDC videos with high-level overviews that feel more like advertisements.

Back then they've at least made attempts to use some open standards, and allowed 3rd parties to fill gaps in the OS, instead of acting like a Smaug of APIs.