I think by "reward" in the context of this discussion on loneliness, OP may have meant the opportunity to meet people, make friends, perhaps hit it off with someone and land a date, if you're single. Not that it's entirely useless/detrimental to spend time at home reading or pursuing whatever solo hobbies you happen to have.

To be sure, there certainly are many introverts who are perfectly happy on their own with no need to get out and meet people. More power to them! But there are many that crave human connection, even if they happen to have many intellectual interests and for these types of individuals, they would be well served at least carving out some portion of their time to get out of the house with the explicit aim of meeting people. And yes, not every such outing will lead to lifelong friends or meeting your next soulmate, but it's a numbers game.