To paraphrase Barney Stinson:

When I'm feeling lonely, I stop feeling lonely and feel awesome instead.

There are lots of good suggestions in here. People just need to go do them. And if there are structural impediments to doing them, then eliminate those impediments.

I wasn't getting out enough during the day because I share the car with my wife. So I bought an EBike and now I go out all the time.

I chose to live in a place with things near by that I can go to.

Whenever I'm thinking, I'd like to go do an activity, but I need something else first, it's usually not true, or the other thing I need is easy to get.

People just need to decide to stop doing things that make them unhappy.