I'm in my late 50s and have been through a lot of shit, and one thing I can tell you is that people generally won't change until the pain of changing is less than the pain of staying stuck where you are. Moreover, you can want something for someone else, and even if it would overwhelmingly make their life better, it'll never happen unless they want it for themselves. People are creatures of habit, and those habits rarely change except when there is no other option.
So what do you do? Focus on something that you can change - your behavior. Understand that they make their own choices, and if they aren't interested in doing things you're interested in (going outside, socializing, etc.), you need to find people who are interested in those things and engage with them. Healthy people grow and change throughout their lifetime, and some people are less able to do that, so you can outgrow your friends. I'm not saying you should kick them to the curb, but rather understand and know their limitations, and budget your engagement accordingly. Relationships, including friendships, are necessarily a 2-way street. If someone won't meet you halfway with effort to keep the relationship afloat, then you should consider why you've been propping things up and match their energy and see what happens. The phrase: "If he/she wanted to he/she would" is something to keep in mind. People communicate not only with their actions, but also with their inaction. Find people who appreciate you and the energy you bring by reciprocating it.
While it can be challenging to make new friends as an adult, it's not that difficult. Learning a new skill or hobby can introduce you to a lot of people. For example, I recently started learning swing dancing, and suddenly have several new friends of both sexes, and a never-ending string of fun social dancing events to go to. It's been a total game-changer for my social life, and I would highly recommend taking classes to learn whatever social dances are popular in your area (swing, salsa, etc.). Of course there are also meetup groups for almost every type of hobby or interest, so you can do something you're interested in and meet like-minded people. Basically, just get out there and do what your want to do, and find people that also like to do the things you want to do.