What the hell am I doing with my life. Why do I spend my time doing things like Reddit and Pokemon Showdown instead of things like writing, meditating, organizing my life, playing piano, writing software for myself, starting businesses? I know what will make me happier. I know what will make me proud of myself. But I don't do it. Instead I do the stupid yet easy thing, even though it feels like letting my soul die.
So... why not try something new every couple of weeks? Try doing something out of your comfort zone an hour every day and visualize how that hour is going to improve your life. Before you know it, you will have some mastery over a different skill in no time at all!
I've been slowly getting out of a very similar situation from the things you describe. The big thing that has helped me is to prioritize building a platform of good habits, upon which you can build skills and projects. For me personally, this is being accomplished by strictly partitioning things in my life. My big time-sink has historically been the internet, so I started by eliminating most social media and by not carrying a proper smartphone. I get (and make) lots of jokes about my ancient blackberry, but after a couple days I really felt like my brain could breathe again. I try to keep screen time at my desktop to 1.5 hours on workdays--timed shutdown programs help a lot with this. To-do lists have also made a huge impact on my productivity--I try to make one at lunch every workday, and though I rarely hit everything on the list it helps me answer "uhh what am I doing again" with "throwing a few stitches in your project jeans" instead of "...reddit". Making priorities of things like journaling, artistic expression, and especially meditation has also been extremely helpful. I took time off of my regularly scheduled hobbies (6 months!) just to work on un-fucking my brain. It took serious mental effort for me to make meaningful progress on this, and it's a battle I've fought for my entire adult life. If a goomba like me can start getting on the right path, though, then so can you. Work hard to make yourself better, but most importantly, be willing to forgive yourself when you fall off the wagon. Dust yourself off and keep going, you can do it.
Because it's easier and offers more immediate gratification. Reddit and Pokemon are gamified to the point of addiction. Read Jane McGonigal's Reality is Broken - her facts are questionable (anyone who quotes Heroditus as fact hasn't done their due diligence) but her perspective is novel.