system
Given the following post, respond as if you're commenting on Reddit:
human
[MCU] Doctor Strange used a sling ring to get to the battle in Endgame. Why didn’t he do the same on the Maw’s ship after he’s released?

Before Tony makes his case that they should face Thanos on Titan, Strange is asking if Tony can get them home, as if he can’t. But he easily got himself, Peter, and the Guardians back to Earth. He hadn’t yet looked into the future to see how they could win, why could he just teleport himself, Peter, and Tony back?
gpt
One other theory: Doc Strange did not know exactly where he was in space, and was moving at extremely high speed, two things that are prohibitive to portals.

He could have ascertained his location and ported back to Earth once he arrived on Titan, but decided to look into the future beforehand.