This isn't like the NFL where nothing can really be done until well after the season is over (Free Agency has a specific start date, the draft is a couple months down the line).
Coaches started scouting high school kids for this years class 3 years ago, and started actively recruiting them 1-2 years ago. And every single person they recruit is someone that fits the needs of the team (you're not spending a lot of time recruiting the top LB talent when you brought in 8 in the last two years, etc...). Notre Dame is even more difficult due to the stricter academic considerations. Not to mention having to completely figure out everything he can about his new team and all of the recruits that were previously recruited by Weis...does he still want them / do they want to play for him / what has to be done to make it all work out.
ND is going to pay him top dollar to turn their program around and every single move he makes is going to fall under the microscope of the college football world. The reports were that he talked to his team in private about what was going to happen, and while I'm sure all of those kids want him on the sideline, I bet they all also want him to succeed in his new job. I'd counter the tantrum above and say, Ask every one of those kids if they hate Kelly because he is going to start a new job, and almost all would say no, they understand.