Because that’s like saying you’ll develop a fuel additive to stop the body from rusting. Physical damage and weakness can’t be stopped by a pill.
And if it's the body doing that, you can, in theory, find a biochemical way to make it stop doing that.
If you rephrase that to correct English then it would make sense. We aren't trying to stop physical damage or weakness we are trying to prevent it from happening. Pills can prevent many things that cause this.