They're simply not taught how to do so in high school.
Read Death to High School English
Why do you care, Steve, you're the Hudson Valley Geologist?
Because I make my students write labs and papers in geology classes - just like you're made to write in real life if you have any job beyond that requiring the use of a deep fryer.
"people who right like this and dont use proper grammer or spelling, sometimes random Capitalization for know apparant reason and, wierd comma use or slang like u see hear in a college paper are surpisingly common in the college."
I swear to God I've read shit like this in a college-level class. (OK, it's a community college, but these students do have high school diplomas!)
I wouldn't hire these dumb asses if I ran a business.