Why are so many tech CEOs former product managers? Sundar Pichai joined Google in 2004 and led product management for Google's client software, including Chrome. He's now CEO of Google and Alphabet. Marissa Mayer worked at Google as a product manager and created its Associate Product Manager program in 2002. She later became Yahoo's CEO. Bret Taylor joined Google as an associate product manager intern and ran the team that co-created Google Maps. He went on to become Salesforce's…