It's plausible that GPT-4 getting worse is just a cash grab by OpenAI. Release a powerful yet expensive to run model, push its transient virality to get people to sign up for monthly memberships, and then replace it with a cheaper to run/worse model to rake it in. Their investment deal with MSFT strongly incentivizes them toward profitability sooner (MSFT gets 75% of their profits until the $10B is "paid back"). So if they want to become independent from MSFT this might be their best bet.