It's because Google was and is still an engineering organisation. For the most part they still don't understand UX or design, and when they do it's in some incredibly maligned product that no one wants.
I'm willing to bet on the opposite. I think it's engineers who understand how the product should work to be useful, but it's the sales and design people which screw this up because "hey, it's cooler / more shiny / will attract new people".
