He should have Gone for Thanos Head but he hit his chest. Then because of this mistake of Thor, Thanos destroyed half the population of the universe
after that Thor went into depression for not killing Thanos
And then he started drinking alcohol and for those 5 years he only drank alcohol because of this, Thor’s weight had increased And he had become Fat Thor
The biggest reason for him to become Fat Thor was his failure
After Avengers Endgame, Thor now embarks on a new journey into the Galaxy with Guardians of the Galaxy
And then it all meets Gorr the God Butcher
The one who has a weapon named Godbomb
Fat Thor: Why Did Thor Get Fat, depressed And Weak in Endgame