It's because they launched this product with an actual reasonable amount of ram (16gb) compared to the 8gb they are still selling MacBooks with. So, if they can't charge you $300 for a little bit of ram now, they instead are going to rape you on storage. Apple is still apple.
Because it's $600 and velcroing an external HDD to a nice new sleek piece of hardware makes it look ugly. Typical Apple bullshit, I'm surprised they didn't develop another proprietary connector.