It's also economics. I think that a cheapish menu del dia works out less expensive than buying food, cooking it and then washing up, all of which is powered by electricity which is very expensive in Spain, and always too underpowered when you need it most. Boy, do they know how to invoice! Also, I'm no chef, despite loving good food - or perhaps because I love it I know how poor my cooking is.
Psychologically, eating out lets you know you're still alive. You see other humans and without any need to engage in pointless chat with them unless you really feel the desire. I usually don't, not because I don't like them, but because I know they have nothing to add to my life that I need or care about. It's been my misfortune to find sport, local gossip and communal booze of very little interest. In most relationships, it seems to be the lifeblood. Booze was okay when I was part of two people, one was always able to drive. Today it would kill me in no time because of heart. Drinking home alone is so, so sad. Anyway, it would still kill me doing it here.
Eating out was great as a couple - alone, I used to find it difficult at first, but now that bothers me not in the least - to be honest, I dread someone I know walking into the same place and joining me at the table. Been through that, even changed restaurants to stop it. Can't say I ever feel particularly lonely, but I sure do feel empty, with a void nobody else can fill. Such is later life alone. I've seen it so often that I should have been prepared, but one never is.