That's not exactly accurate. The other teams didn't develop their own double diffuser when Brawn did and like Brawn did because the other teams knew it wouldn't conform to the spirit of the regulations. Most of the teams were present for the meetings from which they walked away with an understanding of the season's regulations, but Brawn was not one of them. The teams that were present understood the intentions of the regulations, which weren't sufficiently expressed in the wording of the regulations, so Brawn created a diffuser that technically complied with the regulations as worded but not as intended. Brawn had it from the start and planned for it all along while the other teams planned on not having it and didn't have it at the start because they never expected it to be acceptable.