Marvel DC Crossover

Why is Thor fat in Avengers: Endgame  ?

All these people will tell you that he follows after his father, Odin when times got rough,

or as a symbolism of old Norse Kings and what not. But do you want an honest answer ?

Look at this man

He truly embodied his title of God

His power levels were simply off the charts, he was King, he was the strongest avenger, he was  overpowered.

Remember the fight between the main three Avengers and Thanos ?

An epic fight, without a doubt, but you can so easily tell how slow Thor is moving

and how weak he was compared to his prior state.

This was a plot device to allow other characters like Iron Man and Captain America to seem just as powerful as him(Cap getting Mjolnir).

The movie would have ended too early had Thor kept his shape