Netflix questions? Why cant i watch certain movies? Dexter?

So I recently got netflix and i am on the first month free trial and I got really REALLy into Dexter i watched the two seasons that were on netflix in like 2-3 days because i'd watch it pretty much all day but it doesnt have the 3rd or 4th season would they add them eventually or no? Also I wanted to watch like the famous movies that everyone knows about like the notebook, forgetting sarah marshall, the omen, the exorcist and it has them it just says Not Available, why arent they available to me? Is it because i am on the trial? when will i be able to watch those movies and more? Thank YOU!!!