openrouter.ai does exactly that, and it lets you use models from OpenAI as well. I switch models often using openrouter.
But, talk to any (or almost any) non-developer and you'll find they 1/ mostly only use ChatGPT, sometimes only know of ChatGPT and have never heard of any other solution, and 2/ in the rare case they did switch to something else, they don't want to go back, they're gone for good.
Each provider has a moat that is its number of daily users; and although it's a little annoying to admit, OpenAI has the biggest moat of them all.
But, talk to any (or almost any) non-developer and you'll find they 1/ mostly only use ChatGPT, sometimes only know of ChatGPT and have never heard of any other solution, and 2/ in the rare case they did switch to something else, they don't want to go back, they're gone for good.
Each provider has a moat that is its number of daily users; and although it's a little annoying to admit, OpenAI has the biggest moat of them all.