Those programs are the exception and not the rule. Smart was DC at Alabama under Saban. Saban was running that defense and still is. Smart may very well have been content in riding it out until UGA opened up because that's the job he wanted. It worked out that UGA finally let Richt go and the opportunity was there. Those situations are few and far between. It is a profession of nomads and they're all connected in some way. One domino falls, others go down, etc. How many Bud Fosters are running around out there in 2020? It is as much about timing as it is the individual ambitions of these guys.
Pretty much every consistently top tier program over the past 20 years has had a "Bud Foster"... a long tenured assistant responsible for culture, recruiting, coordinating a side of the game, or some other key aspect of the program. The ones that haven't have been flashes in the pan or rudderless floundering around like Tennessee or Michigan.
Alabama = built their way to the top of the ladder with Kirby Smart as DC for 8 years. Their most consistent success (3 championships in 4 years) and best defense came with Smart at the helm.
Clemson = Brent Venables is still there.
Ohio State = Marotti has been there since Urban got the job and is continuing under Day
Is it "rare" for programs to have long-tenured assistants? Sure. Do the Tier 1 programs all do that in at least some key positions? Yep. And that's what Notre Dame should be aspiring to do. It also allows you to groom people in order to promote from within and continue continuity if/when they
do eventually leave. Like how Ryan Day went from co-OC/QB to OC to HC. Or how Tony Elliot went from RB to co-OC/RB to OC and has been at Clemson for 9 years.
It is naive to think that these guys don't have other goals and ambitions outside of being lieutenants for Brian Kelly. Tommy Rees is a smart kid. As his offenses continue to perform, he's going to get offers for higher title and higher salary. It isn't realistic to think ND can afford to keep him around forever and that he'll be content with being offensive coordinator with an added title on of associate head coach or something made up down the line. It's the nature of the beast.
To be clear, this isn't even close to what I said. I also specifically didn't list Tommy anywhere for a myriad of reasons.
Again, I think our fan base makes this out to be a far bigger deal than it is. You want as little turnover as possible, but in the end, it's part of the business and you deal with it. To some degree you do what you can to keep people, but within reasonable limits in terms of time and money.
Our fan base makes a big deal out of it because they want to keep building, and they want the school to function like a true Tier 1 program. Yes, that means your assistants (especially offensive ones!) will always be attractive and will get poached. But all of the Tier 1 programs -- I'm talking about the four that make up 70%+ of all CFP appearances between them -- find ways to not just retain key assistants but to generally promote from within to continue continuity. Whether it's a Dabo + Venables marriage, or grooming Tony Elliot under Chad Morris, or Saban having an army of analysts so he can easily tab the "next" guy without having to scour the market, or Oklahoma having a transition plan in place for Bob Stoops, or etc. etc. there is a right way to do things. Part of that is paying your key assistants that you
know are good coaches top dollar with secure contracts so that they are retained as long as possible and don't leave unless it is the "right" promotion
plus having a plan in place for when they
do leave. Being nonchalant about assistants is what ultimately undid Mack Brown at Texas (and he's talked about this quite a bit in his stint as a television personality), as well as many other ascending programs or "dynasties."