Why do most CNA's usually become a RN instead of a LPN?

I am currently a NA but i am confused on what i want to do next go to LPN school because it's only a year or RN school. Before i became a NA i told myself i was going to go up the latter one step at a time but now im thinking is it worth it. A lot of people tell me to go straight to RN school. What should i do. HELP!!!!!!!!!