"...supposed to hit every print..."
Oh god no. Your single line would be a mere blur through the millions of trades in a day, and market price info would be slowed to molasses as everyone, in essence, applied for by-tick timeXsales data. So, how to speed things along?
4 data points are collected for each defined cut of time -- the opening price, the high, the low, and the closing price -- ye ol' OHLC. Of those four, on which would you base a single line?
The Open is the least relevant -- if the defined cut of time is a 1-day 'candle', then the open would put your line chart a full market day behind.
The High is not relevant -- it's just a momentary thing...and EVERY other trade was less than that!
The Low? What if the price was climbing all day?
So we're left with the Close -- which handily enough, is also the *latest* information for that time period. ("Yayyyyy!")