Let's just be candid. There are a lot of people, including some officials, that confuse the ability to run back an interception from the end zone with the inability to run a kick back out of the end zone. As stated above, there is no enforcement reason to bean bag the interception. But with the momentum rule in play, it's not a bad habit. Of course, if they run it back 100 yards, someone has to go retrieve that sucker.