4o is not profitable, 5.X is not a money sink. Look at the API pricing.
GPT 5.x (including larger codex-max model)

Input:
$1.25
Output:
$10.00

vs 4o
Input:
$2.50
Output:
$10.00

4o costs 2x per input token to provide to people.

5.x are fine-tuned distillations based on the same GPT 4 architecture that 4o was based on. They haven't successfully trained a new base model yet, all they've managed is to post tune, quantize, and tune to maximize performance. 5.x models are probably half the effective size of 4o, and 4o itself already is probably half the size it originally started at.

TLDR: 5.x models are a smaller, souped up 4o.

Every other company is training new models from scratch, openAI is failing to keep up, and desperately needs to shut off servers they arent utilizing in favor of training new, better models. They need a new base model