>>149212735Because it's THE teamup.
Originally, when Dick was on the Titans, and Doug Moench was tryign to see if he could age down Robin to do a classic Batman and Robin set up, editorial proposed the way to split the difference was to make a new sidekick. But, originally, they didn't want to take away Robin as a mantle from the Titans(since the Titan book sales were WAY bigger than Batman at the time), and didn't want two Robins, they were going to make Jason take up a new mantle.
It was quickly scrapped, because Moench argued that Batman and Robin is what everyone knows as the dynamic duo, and any attempt at making a new sidekick would always be fleeting. So the only trace of this was Jason's proto costumes.