Number 1 is done like that as it’s eaiser to package in the standard sandwich box
I'm not sure what sandwich box you're referring to. You mean like the premades some stores sell...
I think it's likely the other way around. The boxes are made to show off the sandwich cut like that.
From a visual appearance #1 looks more appealing because it has a longer cut line so you see the filling more and it looks more filled. It's no surprise stores sell it cut that way because they're trying to win your eyes.
From a practical standpoint cutting into rectangular halves might be better because less surface area for contents to fall out of the sandwich .
It comes down to what you're trying to do.
If you're trying to sell a sandwich or look fancy/appealing, a diagonal cut is probably better.
If you just want to eat a sandwich and insist on it being cut (but really why bother), straight across the middle into rectangles is probably more logical.

