Garrett was still technically coach when they were interviewing for the position. They knew already who they wanted. Contracts take longer than just a couple of days. This has been in the works since before the season ended, I guarantee it.
That's the worst decision I've ever heard by the Giants. Why? Because one of the rising things in the NFL is game-time analytics. This is like moneyball for football. Basically it's a data-driven assessment of any given situation and allows a team to make calls based on said data instead of "gut feelings". The poster child of this are the Baltimore Ravens. You can read about it a little bit here. Looking at their stats, the Ravens went from 25th in the league offensively in 2015 to first this year. All because they implemented an analytics-minded approach and are sticking with it.
Now look at Garrett, who scoffed at analytics and said that they are not valued. He's consistently made questionable calls on the offensive side of the ball and clock management. As a head coach he was 85-67 (.559) with ridiculous talent on the team.
He's a decent person but not a coach I'd want to have in 2020 or going forward unless he radically changes his outlook and style.
Packers vs. Titans - Intriguing matchup: old veteran QB vs. QB with a second wind; team looking for that next SB vs. team denied a Super Bowl for so long. (Scarily, this would feel a lot like the setup to SB XXXII for me...)
49ers vs. Chiefs - Surprise team from the NFC vs. The New Kids On The Block.
49ers vs. Titans - The Super Bowl You Thought You'd Never See(tm)