The lines put out by vegas is to try and get as close to 50/50 betting as they can get. If they set the line of the Oregon/Georgia game as a pick'em -- all the money would be bet on Georgia. So they try to find a line to set where people will bet on Oregon too.
If it opened at 14 (I don't know what the line actually is -- I'd guess it is in the 17-20 range, but i will say 14 for this example) -- and at 14 overwhelming majority of the money was being bet on Georgia. Guess what happens. The line will go to 14.5, 15, 16, etc. until the books start seeing more money going on Oregon.
The spread is nothing more than an educated guess to where the books believe they will get equal action from both sides. The last thing the books want is to have all the money to be on one side or the other.