Earlier quoted context omitted.
To understand why certain products, which are seemingly unrelated to Google's core competency, have stayed with Google and haven't moved on to Alphabet, or why Google created a product such as OnHub and not Nest, you have to realize why all of these product are under Google - to track all the data that goes through them under the same generic/unified "privacy" policy, and then feed it into its advertising system. Tha…
I hate to burst your bubble, but it's actually just a branding thing, and has been in the works for much longer than anyone involved knew that Alphabet was going to happen. The team that built this is part of the same company as Google Fiber (disclaimer: for which I work), which is in fact no longer part of Google Inc.
I've heard it's mostly a liability thing. When projects like the self-driving car were directly under Google, Google's assets were fair game in any lawsuit over that technology. With the current setup, liability is siloed in each legal entity which gives the cash cow, Google, more protection.
More here: http://www.theverge.com/2015/8/13/9149431/alphabet-google-co...