Sure there are exceptions like coach k.
But:
Source Wikipedia:Coach K's first 3 seasons at Duke

17-13 (ACC 6-8)
10-17 (ACC 4-10)
11-17 (ACC 3-11)

Those numbers these days would put your job on the hot seat. Who knows what may have happened if he got fired there.
And I know this might be for another topic, but since Calipari started recruiting one and dones, suddenly coach k starts doing the same after a few early exits in the big dance.

Coach K also coaches practically a new team every year...

Every coach coaches practically a new team every year. But Duke has been known for not having players declare after 1 year with some exceptions.
Look up what Coach K alledgly said to William Averys mum when he declared early.

Coaches these days know that virtually all of the top players in the country (i.e McDonalds all-americans) want to go to "one and done" type of programs.

After Cal started doing it, Coach K followed suit (when previously he wouldn't ever consider one and done players - the Avery example is evidence of his past disdain for the one and done system) because that was the only way the best players would come to Duke i.e. if he sold the one and done ideaology.

Interesting how he had to adapt to keep pace with modern recruitment policies.

As an aside the Avery example was horrible. Coach K stepped over the line. Avery's family was very poor and I don't think it was ever right for Coach K (and all his millions) to comment on a kid whose family had absolutely nothing and needed help.

In today's coaching world, there is no way that he ever sees out the 3rd year. Coaches get two years max..if a Duke coach failed in his first two years and then went 11-17 in his 3rd year, no way the college is getting him back.

I think there's a number of factors to consider. Whether the coach is a fixed ideas person, or whether they can negotiate with others. Fixed ideas coaches get stale pretty quickly. Another factor is assistant coaches. A good assistant coach provides data and intelligence on their squad as well as the other squad. Having a good assistant that challenges the coach's thinking prevents them from becoming stale.

Basically, if the coach is constantly asking themselves "how can I make me and this team better", then they'll stay as fresh as a Scottish morning in winter, however, if they are fixed in their ideas, then they'll stay as fresh as a bucket of prawns in the sun.

ask phil jackson
ask eric spolstra
ask Red Auerbach
ask George Karl 6 yrs with seattle, 5 with bucks and 8 with nuggets
ask doc rivers 9 years with boston
ask mike fratello 7 years ATL, 6 with cavs, coached Ukraine since 2011

As I said in the original post, if your winning titles or in contention then nearly everyone is happy so disregard the Popovichs, Jacksons, Aurbachs, Docs etc examples as above. Will be interesting to see how far Spoelstra will last now without Lebron.
George Karl is a good example of lasting long term but I think he has runs on the board in terms of sustained winning in different franchises.
And a Mike Fratello reference, wow.
I think in years past coaches were viewed as long term hires, but nowadays the players have the power mainly so if a star player wants a coach gone it's easier to sack the coach than to get fair value for the player.

And I would say college coaches have a whole other side to their coaching area than your NBA /NBL type coaches, after all college coaches are supposed to develop the whole player as a person and an athlete, the rest are supposed to get ready made ones