Most people like visiting restaurants as a break from the regular day-to-day preparation of meals at home. They typically enjoy (most times, though not always) the ambiance of eating out at a quality restaurant, whether fine dining, casual dining, or fast food/take-out type places.
Eating out in restaurants gives one the chance to try a variety of fare, whether unique dishes from different countries, or regional foods using ingredients sourced from farmers and such close at hand to where a diner lives. Restaurant eating also gives an individual the chance to try, first-hand, recipes from chefs who've gained a reputation for exotic and fanciful food offerings.
In addition, eating out in restaurants is something most people enjoy because it often inspires them to try new recipes and variations of recipes at home. Furthermore, eating out in restaurants is popular because it is a time-saver when on the run going to and from different activities and responsibilities. It's easy to run into a fast food place and the like for a quick meal while on the go.
Moreover, people enjoy eating out in restaurants because it becomes a social event, especially if it involves a local restaurant where they generally run into people from their community and engage in conversation while enjoying good food. The act of eating at a restaurant, within one's community especially, also contributes to the local economy. It helps the restaurant and the other businesses in the community dependent on the restaurant, such as food, drink, and packaging suppliers.