The article explains it, but it's not 100% clear why the extra step was needed.. "Google co-founder Larry Page announced Alphabet two years ago to foster new businesses that operate independently from Google. Technically, however, those units, called the “Other Bets,” were still subsidiaries of Google." With this new change, XXVI Holdings will hold the equity for all child companies, rather than Google still being the owner.
Until now the only Alphabet subsidiary was Google Inc. The other bets were still Google Inc subsidiaries. This move brings them up a level and separates them from Google.