That tradition was created by engineering limitations and, showbiz has moved on since then.
Actually, in the NFL and NCAA (the posts you showed), the posts are at the back of the end zone. They've always been there, and have nothing to do with engineering limitations. As well, in the NFL and NCAA, the in-goal area is fixed at 10 yards, so no matter where you play, it's always at 10 yards. If you did this in rugby, depending on the pitch, you could have posts 20m behind the try line or 5 meters behind it. You probably would prefer posts as pictured below that are used in the CFL. They're also the posts that we use for our varsity matches and trainings as we play on the Football fields of our universities. I'd have no issues with changing to those posts. I will say that they move quite a bit more than the standard rugby posts, and on a windy day, they'll be swaying as the ball is flying through the air during a kick. This isn't really an issue for football as they're always right in front, but if you're on the touch line, a 6" sway in the posts could be critical.
I posted a link to the image as, for some reason, I've been limited to uploading images no larger than 25kb...
https://www.campusvibez.ca/wp-content/uploads/concordia3.jpg