You’re right. I’d suggest changing your last question slightly: why bother worrying anymore? If you can acknowledge these problems, recognise you’re powerless, and instead focus on your own personal happiness and wellbeing, you might find a bit more purpose and a little less doom and gloom in your life.
Yes, I feel pleasure when lifting weights. It’s good to feel powerful, and it’s good to feel like I’m getting stronger. I also get pleasure from knowing I can do it and that I’m dedicated and can keep up the routine. So I suppose it’s mostly mental pleasure, but physically having that feeling of power is great at the very least.