I think most of this is just downstream of the Mac being eclipsed by the iPhone in terms of Apple’s revenue. The Mac just isn’t critical to Apple’s business like it was in 2009 when Snow Leopard came out. They would have started development on SL in 2008, when the iPhone was still a fairly niche product and there wasn’t even an App Store.
Now, ios gets the executive attention and it will generally get the best developers assigned to it, and the Mac has to live with the scraps.
Yeah I think this is the one, in terms of number of users, revenue, etc. The iPhone is more than 50% of their revenue, Mac is only ~8. Lower volume and higher price, but it doesn't come anywhere near their phone. Same with tablets, although they share an app revenue income stream with the iphone which makes up for the difference in hardware sales.
Now, ios gets the executive attention and it will generally get the best developers assigned to it, and the Mac has to live with the scraps.