I'm sure most of us knows Nightwing's origin story. Dick Grayson as Robin was spending a little too much time out of Gotham with the Teen Titans for Batman's liking and when he was late in helping Bats take on Clayface (As seen in Nightwing: Year One) that was the final straw causing Bruce to not only fire him but also making him give up the Robin identity. Dick then explored his roots for a while and had a talk with Superman which inspired him to branch out on his own and become Nightwing.
In Young Justice though, there's been no mention of the Teen Titans and I'm pretty sure that the team doesn't exist (I could be wrong). Not only that though but Batman himself is the YJ team's commander giving them missions and assigning roles etc. So obviously if Batman's the one giving out the missions he can't be upset or surprised that Robin's not always gonna be around because he himself is the one that sent him away. In some episodes not involving Robin the rest of the team (usually Wally) specifically says they're off being the "Dynamic Duo" so it's not like he didn't help out anymore.This means there would have to be a different reason for Robin becoming Nightwing other than him 'being fired for not being around enough'.
So what could be the cause of him going from Robin to Nightwing in the YJ universe? Was he still fired? What was the reason? If it was for the 'not being around enough' reason then why is Tim Drake also a part of YJ?
Hopefully all this will be answered soon.