Kelly was largely successful at Notre Dame and seemingly knew that so long as his teams fared better than his predecessors, he was in good standing. And that's what happened during his tenure.
Kelly appears to be calculated in building his coaching resume, accepting jobs at underachieving programs, knowing he can improve the program on his watch. Taking the job at LSU (6-6 this season) for a ton of quid, and knowing he can get them to 9-3 or 10-2 in short order, is exactly the low hanging fruit that Kelly has always sought. [Whether winning 85% of the time at LSU will be good enough is another question, but I don't think Kelly cares. He has now made bank.]
Is there any doubt that once Kelly checked the box of surpassing Rockne in wins, that is was time for Kelly to move on to greener pastures, and check another "I improved an underachieving program" box. And, although Kelly knows that "I'm here to win a national championship" is the correct messaging, I am not sold that he has ever meant it.
Kelly found a nice sweet spot in his career -- improving above average programs to a Top 10/ Top 5 caliber program -- and knowing that would be good enough.