It's because people like choice and control, and "5.2" vs "5.2 thinking" is confusing. Making them "5.2 instant" and "5.2 thinking" is less confusing to more people. Their competitors already do this (Gemini 3 Fast & Gemini 3 Thinking).
ChatGPT 5.2 Intuitive
ChatGPT 5.2 Ponderous
“I had this dream the other night…” – https://www.youtube.com/watch?v=6gYIbMwswKM
ChatGPT 5.2 Intuitive
ChatGPT 5.2 Ponderous
“I had this dream the other night…” – https://www.youtube.com/watch?v=6gYIbMwswKM