As another poster has said, much of the "junk" is not junk.

The parts of the DNA with known functions encode either proteins or RNA molecules, being templates for their synthesis.

The parts with unknown functions include some amount of true junk caused by various historical accidents that have been replicated continuously until now, but they also include a lot of DNA that seems to have a role in controlling how the protein or RNA genes are expressed (i.e. turning off or on the synthesis of specific proteins or RNAs), by mechanisms not well understood yet.

>Second, what's even more crazy is that roughly 98% of that DNA is actually non-coding.. just junk.

I think it's a myth that non-coding DNA is junk. Say:

https://www.nature.com/articles/444130a

>'Non-coding' DNA may organize brain cell connections.