[Barrin92]

Google didn't change its org structure for consumer-facing rebranding purposes. It was a move for the market/investors, to separate out more clearly the (lack of) profitability of individual sectors and acquisitions of the company that don't happen to be ads or search. Alphabet was about creating internal transparency.

[jacquesm]

That's the story. At the same time their former CEO made quite a few statements that did not sit well with the management of the daughter companies, Google's reputation is such that some distance really doesn't hurt in the PR department.