I think that kind of inertia mostly lasts as long as there is no financial incentive to move. A ChatGPT user who is not paying anything to OpenAI is of little benefit to them, and has little incentive to switch. However if OpenAI start trying to make money off those users by adding advertising, or removing the free tier, then things may change. Google can afford to subsidize chat from their other revenue streams, but OpenAI can't.