At time it was a defense against Microsoft embrace-extend-extinguishing the web through their dominance with IE. Remember ActiveX, VBscript in the browser, etc?
The threat of that had already been greatly reduced by the time Chrome came out. Firefox was quite dominant, and IE had become much more standards compliant.
I just checked and seems like IE was down to around 60% and Firefox up to a third when Chrome launched (not sure how long before that the project was greenlight). So it probably still played a role.