So he can look like he's getting something done. Almost everything Trump campaigned on was a pipe dream or he has managed to quickly derail if it was even remotely possible. So he needs something to parade around in front of his base even if it's entirely symbolic.
For another example, look at the weird attempted rebrand of existing border fencing as "bollard walls" a while back because the border wall he campaigned on is never going to happen.
So he can look like he's getting something done. Almost everything Trump campaigned on was a pipe dream or he has managed to quickly derail if it was even remotely possible. So he needs something to parade around in front of his base even if it's entirely symbolic.
For another example, look at the weird attempted rebrand of existing border fencing as "bollard walls" a while back because the border wall he campaigned on is never going to happen.