In 2015 Alphabet was created as the holding company for Google and several other companies previously owned by Google. At the time I thought the name would be more appropriate for an online preschool, not a technology-driven corporation.
Perhaps the consultants who chose "Alphabet" were advised about association by Julia Quinn. Julia Quinn is the pen name of a best-selling American historical romance author. She says she chose her name so that her books would sit on bookshelves next to those of the best-selling romance writer Amanda Quick. Using Alphabet as a company name follows this formula for success, as "Al" is close to and comes before "Am" (Amazon) and "Ap" (Apple). So, in lists of highest market cap, most-admired companies, or donors to nonprofit institutions, Alphabet, by playing the alphabet, "front runs" these other heavy weight companies. My kids used to call this kind of behavior "budging in line".