then every casual user would switch instantly to Gemini, or the most convenient alternative
You misunderstand. They are going to force everybody to pay $5, then force everybody to use chatgpt. 8 billion times 5 isn't much money, but the advertisers will surely pay a lot for that many captive eyeballs!
(I have no MBA either)
At this point why forcing people to use the service, if you can forcefully extract these eyeballs and then sell them directly to advertisers in large enough jars?
My jurisdiction just legalized sports betting (or something similar, I don't care all that much about what specifically got legalized), and there's been an immediate explosion in gambling ads across various media formats.
A very common refrain is "these ads are terrible, but I refuse to consider paying for any ad-free subscriptions."