1 People like to eat out when they are tired and have no energy to cook at home.
2 Also people can try those dishes which can't be cooked at home because the recipies for them are too challenging or time-taking.
3 People need to socialise - and eating out with friends or relatives can be a perfect way of spending time.
4 And of course if you eat out, you won't have to clean the kitchen and do the washing up after the meal :)