Sundar Pichai’s appointment this week as chief executive of Google parent Alphabet Inc. effectively shifts the focus back on the company’s advertising profit machine and away from its “moonshots” and other potential new businesses.

Mr. Pichai’s promotion late Tuesday amounted to the biggest managerial overhaul of the internet giant since 2015, when co-founders Larry Page and Sergey Brin created Alphabet as a parent company above Google. Their goal then was to make Google and its highly profitable advertising businesses just...