It seems like that's what they were doing with DeepMind for the last decade. But it's also possible DeepMind as an institution lacked the pressure/product sense/leadership to produce consumable products/services. Maybe their instincts were more centered around R&D and being isolated left them somewhat directionless?
So now that AI suddenly really matters as a business, not just some indefinite future potential, Google wants to bring them inside.
They could have created a 3rd entity, their own version of OpenAI, combining DeepMind with some Google management/teams and other acquisitions and spinning it off semi-independently. But this play basically has to be from Google itself for their own reputation's sake - maybe not for practicality's sake but politically/image-wise.