1: Faith that our lives aren't pointless. If there's nothing after death, then we are little more than bipedal invasive creatures that destroy everything we touch.

I think it's akin than choosing to be drunk because it makes you happier. Bringing comfort does not make something true.

2: Moral compass. If there's no point to life other than random spontaneous creation of life due to hydrocarbon stacking in an unique fashion, followed by eons of evolution, than why punish murders/rapists/thieves? They are following their genetic predisposition, after all, and in the end (the "big picture"), there's no repercussions if we live only to cease living.

I see it the opposite way. Our lives matters more because there is nothing else. It makes them special. Otherwise, you're just doing time until you reach the afterlife.

My question is this: why is it assumed that Christians only believe in pure creationism? There's zero cause for this, yet the myth persists.

Because many do. I'm not very interested by evolution and would in fact almost never talk about it if creationists didn't bring it back so often.

why does everybody assume that we think the world is only ~6000 years old?

Again, many do.

how does the more accurate interpretation of the age of the earth clash with what science estimates?

A better question is "Why is there zero knowledge in the BIble that wasn't available to tent dwellers of the time?" Being an all-knowing God that cares about my creature, at the very least, I'd teach them the importance of hygiene.