Losing weight and exercising are two of the very few things that I'm capable of doing right now in terms of self-improvement, and I have been making an effort the past few weeks. Yet for the life of me I cannot think of why I should, so the motivation is very unsteady. So I'd appreciate some motivation to do so, though if it's something obvious I'll probably get argumentative.
Well, it is quite literally for the life of you. Your health is your life and your life (And your ability to control the paths you travel through life) is all you have. Exercise is probably the #1 thing you have to do if you value your health. It isn't just about looking better or being attractive. It can be the difference between having a stroke at 60 and living in relatively good health for much longer.
Even if you're depressed and feel like you don't want to live, you might change your mind someday. If you don't invest in your future health right now you might not have it when you decide you want it.
It might not seem like a real tangible thing if you think of your future health as something that is decades off but when the time comes and "someday" is right now, you can't go back and convince your past self to care.