[extension]

But no new platform developer ever seems to get that

I think everyone gets the value of cross-platform development, but in reality it's very difficult to achieve without enormous compromises and history tends to plot against it.

Apple's platform (Objective-C/Cocoa) can be traced back to NeXTstep. In 1988, it was the most progressive thing out there and some would say it still is. Apple leveraged their existing technology and ecosystem through OSX and all the way to iOS.

But the rest of the industry went in other directions. Objective-C/Cocoa would have been a strange choice for Android and would only have made it even more vulnerable to Apple's formidable patent arsenal. Instead, Android uses Java, which is also an attempt to leverage an existing ecosystem. But Android's fairly novel models of user interaction and application lifecycle required a whole new API. And Google had to reimplement the VM to avoid license fees, which still wasn't enough to avoid a patent attack.

In summary, as long as we have a) innovation and b) lawyers, we will constantly have to learn new development platforms which may not always be entirely novel.