It's not intentional. It seems to me a matter of positioning. It seems to me that you don't know what the right position is until the guy slides. He might slide inside the catcher and he might slide outside. If it can become the standard for the first base ump to follow the play home, the home plate ump can position himself for the outside slide, and if the guy slides inside and he's screened, point to first base ump to ask for help.