If you have the full outputs, it might make it easier for competitors to distil the model or reverse engineer the full process.

It may also be that misaligned responses can be in CoT which OpenAI does not want to show to users.

Not revealing actual thinking traces prevents mdoel distillation on yhe actual output (thinking traces are a key part of the output) which makes it harder for conpetitors to catch up (a moat).

Being currently in the lead in a category is not a moat,a moat is whatever creates a barrier to competitors catching up when you are in the lead. Merely being in the lead is not a moat except in a market with strong network externalities.