2. Not everyone has a nice entertainment system in their home, if your TV isn't good or the sound isn't good or you got a DVD instead of Blu Ray or you had to stream but have crappy internet (etc).
3. If you don't control the TV you have to watch whatever is on (parents/teens fighting over the the only TV). Maybe less common now but not everyone has multiple TVs.
4. It forces me to carve out the time to watch/finish the movie because I don't get to just pause it and get distracted.
I go if I want to see the movie badly (and only on a specific day when they reduce ticket prices). I also like the gigantic screen and loud noise. I don't usually remember a movie by the time it's out of the cinema and so never remember to watch it later.