On the off chance that your question is a serious one, I shall reply seriously. Because the supreme court, which is charged with interpreting constititional issues, has decreed that the constitional right to bear arms does not require every household to have a basement full of military and nuclear weapons, but does require that the average, non-felonious citizen has the right to carry a weapon suitable to protect himself, his property and his family.
so they're interpreting the constitution as they see fit. what is 'suitable'? who are they to say that i shouldn't have a rpg in my basement?