In Avengers: Infinity War, why didn't Thor choose to go to Titan right after the forging of Stormbreaker?
What prompted him to go to Earth instead?
Thor had no idea that Thanos was going to rendezvous with his flunky on Titan. He did know that Thanos was first going to Knowhere to get the Reality Stone from the Collector (a relatively easy task by all accounts) then heading to Earth to get the other two extant stones. This seems, to Thor, to be the most likely place to intercept him.
Thor's voice was detached and elsewhere. He still needed time to grieve and process his loss. Now was not that time. He soldiered on. "The Time and Mind Stones are safe on Earth. They're with the Avengers."
Thor contmued, "As for the Soul Stone, well, no one's ever seen that. No one even knows where it is." As Thor continued, Gamora turned her gaze to the ground at her feet. The mention of the Soul Stone seemed to make her very nervous. "Therefore, Thanos can't get it. Therefore, he's going to Knowhere."
Stormbreaker's Bifrost capabilities offer the unique opportunity to get to Earth before Thanos does, cutting him off at the proverbial pass.
Giving Rocket a withering glare, Eitri explained. "It's a mold. A king's weapon. Meant to be the greatest in Asgard. In theory, it could even summon the Bifrost."
At the mention of this weapon, and the possibility of wielding the Bifrost, Thor turned quickly. If they could use this weapon to cross the Nine Realms, he could race Thanos to Earth and stop him.