I'd say because Google is clearly not interested in customer service. If they were, you'd not see all the stories of people unable to contact them to resolve issues with so many of their services.

So, why trust them with something as important as your email when they fail at other things?

Personally, I use a gmail account for non-important communication, and my primary remains a Yahoo account. I've never had a problem contacting a live person with any Yahoo service, or getting back a response that actually shows they read what I wrote.

Customer service is an area where Google could learn from yahoo, but I doubt they care to implement such an infrastructure.