The ONLY purpose of the spread is to even out the money. They don't change the spread with information, they change the spread when more people are putting money on one side. Too many people think that the casinos gamble. They do not gamble, they move a lot of money and take the vig. If I could take millions of dollars from one group of people, give it to a different group of people, and keep 5% I would do that too.
I agree that attracting even money on both sides guarantees a profit. But in reality, there are plenty of ‘lopsided’ betting matchups. Books may adjust the line in an effort to ‘balance’ action by drawing new money on the other side.
If they keep the line unchanged, they risk exposure on one side, but if they move the line (potentially significantly), they risk arbitrage on the other side and even more exposure on middling opportunities.
In terms of how to best manage risk, that usually comes into play by reviewing who is taking the action. But they will absolutely take risks from time to time since exposure is seldom ever truly balanced.
The fact that nearly all the handle (at least at fanduel) is on Miami and the line is unchanged - actually slightly down from 11.5 to 10.5, I interpret that as they have respected action on GT and are willing to take the risk.
Edited to add, they absolutely change the spread with new information. This happens all the time. In football, a perfectly healthy QB that gets hurt right before a game will adjust the spread. In baseball, lines are very sensitive to starting pitchers… a solid pitcher that gets announced as not starting will affect the line. These will look like step changes - and are not based on action. They’re based on algorithms of how much each player is expected to contribute to the outcome.