The specific root cause is Google's practice of promoting based on product launches; it literally doesn't matter whether that product goes on to be successful. This practice creates a strong and perverse incentive to continually launch new products while discouraging iterative development of existing products.
I've never worked at Google, but... didn't Larry Page announce a full-blown program to fight that like 3-4 years ago? Work on features/depth rather than new products?
He can launch programs all he wants, but unless that trickles down to management, and the incentives are aligned to at least reward iterative development as much as launching new products, it's not going to change anything.
Do you have knowledge or experience from within Google? or is this your own conjecture from the outside. My perspective as an outsider is that you are right, but I'm just curious if you have any special insight.