Three big things, from most to least obvious:

1. They own openai, which is a ponzi scheme.
2. They are spying on you. Obviously. This is a better excuse to do more of that more openly.
3. This creates a corporate controlled abstraction layer between you and everything you do with any networked device, puts more decision control and discernment in the corporation's hands. When Amazon tried to move to voice based ordering, it was on this same logic; that you would say 'alexa, order toilet paper' and they would choose the toilet paper to order based on what's best for them-sponsored, most profitable, etc, like you can only buy things from a selfish hyper sociopathic genie. LLM based ux doesn't just put the corporation between you and products, but between you and all information, between you and truth.