Which has happened a lot of times in the past, as has the League managed without Superman, Wonder Woman and even the Martian Manhunter. Likewise, Robin is not a mandatory of the Titans, his presence is great, but the team is bigger than him.
And I am rather glad he didn't, because it finally gave W/P's original creations a chance to be something other than the subordinates to the offspring of greater names. Also, you dont know in what capacity they are being introduced as now, they might as well be the enemies.He should have just used the more iconic characters from the start if he was just going to cram in legacy characters in the next volume anyway.
Because you don't need to explain where Robin is from if it hasn't been changed. Plus at the time the TT cartoon came out, JL/JLU was still a thing as far as I remember and kids aren't that stupid they cant work out where Kid Flash is from.The Teen Titan cartoon used Robin and other legacy characters without the need to explain where their legacies came from.
However in this book, the background was changed; there is no Batman, Flash or Wonder Woman, ergo their sidekicks are going to be more difficult to introduce in a natural fashion.
Because they actually could be around without them?