He obviously didn't want anyone else wielding it at the time. The thing's made out of Groot's arm.
MCU writers
Jackson Jenkins
Grayson Collins
He actually does
youtu.be
at the 4:07
Looking at this scene now. It's definitely Thor being cocky about himself being Asgardian
Thomas Allen
#1 It's not as if Thor would actually know since he didn't forge it
#2 Captain is no mere mortal
William Rodriguez
I can't for the life of me remember that line at all. It wouldn't be the first time the MCU stopped giving a shit about canon
Asher Miller
They are going to fight an all powerful evil. There is no reason for Thor to NOT want the whole team to have Asgardian weapons. It's shit writing period.
Josiah Wright
You know characters are allowed to lie and exaggerate right?
Nicholas Anderson
Especially after he had just watched his brother die and lost everything.
Landon Nelson
Or you're just taking things at face-value and trying to be contrarian?
Angel Russell
It's Captain fucking America.
Jaxon Cruz
Also, Stormbreaker's handle was made with a Groot branch