Why are my big brothers so overportective?

ok im 13 i have two brothers one 17 and the other 25 we all live to gether (we are country people so they are redknecks)so one day they went huntin and i invited my boyfriend over and we were makin out in my room and i guess my brother for got somthin but any ways he walked in my room i didnt here him come in he walked in on me and my boyfriend kissin and he yelled at us and punched my boyfriend and kicked him out guys if your overprotective over your little sister please tell me why