If they release before GPT-5, they don't have to compare to GPT-5 in their benchmarks. It's a big PR win to be able to plausibly claim that your model is the best coding model at the time of release.

Could it be nobody wanted to be first and overshadowed, nor the only one left out - and it cascaded after the first announcement? My first hunch, though, was that it had been agreed upon. Game theory I think tells us that releasing same day in the pattern ABC BCA CAB etc would be lowest risk and highest average gain?