Why not force awareness of things during vipassana? I have heard a lot about vipassana just being mindful of what happens to come up, not looking for more things to notice. However, if we compare meditation with e.g. lifting weights, when you start, you lift (say) 50, so even though its harder, you add 20 more... Then when you normally just need to lift 50, its way easier because you've been working out with 70. My question is, why not do that with meditation? I'm curious why some people don't think it's the thing to do.

As in speed noting, if I can be aware of everything all at one time constantly isn't that being fully aware?  If I can see even the most minute details of the current reality effortlessly through pushing my mental ability during meditation, looking further into things to note more things and staying aware of them all at one time moment by moment till they pass away.  Until you lose track but then try to remember to be attentive to those that remain and notice the new. 

What is said about mental "exercise" as a developmental practice?
The mental exercise the be able to note everything is developing Concentration and Wisdom. These are tenets covered in the Anapanasati Sutta and (Maha) Satipatthana Sutta according to the Theravada Tradition.