Why is that? Serious question.
When I took my current position I replaced a guy that was widely disliked as a manager. He was often autocratic. He came off as aloof to many employees. He didn't respect the plant... and people sensed it. He kind of made my job easier. The first thing I had to do... is not be him. The culture changed immediately partly because I showed them respect and liked them. I also took care of a couple of long term personnel issues that had poisoned the team.. One year in... we set plant production records.... by a wide margin.
I'm about 2.5 years in now and we're working on fairly fine points. We're elevating the standard for guys who have been "acceptable" but aren't the performers we need.
It really doesn't take that long to "change culture" in big ways. Heupel has already made an impact. Kids are pretty obviously "having fun again". Integrity and unity seem to be the two pillars of the coaching staff.
If you've ever worked for a liar and then seen them replaced with someone with integrity... and watched the change around you then you understand what I'm getting at.
I don't have the answers as to why. I will give you a few guesses later. But, I'm just going by what I have observed.
And the exceptions to the rule are situations like Steve Spurrier at Florida. Why? Because he was playing the game completely differently and that overcame a lot of issues. However, as good as he was, Florida ran into two teams that were way more talented that they had to play on the road. And they got their rear end served to them on a platter both times. The other examples are people who took over good situations. Urban Meyer at Ohio State, Tom Osborne at Nebraska, Barry Switzer at Oklahoma as an example. Another exception is General Neyland himself, but I confess I don't know what was happening in 1926.
But, Nick Saban went 6-6 in his first year at Alabama. Dabo went 9-5. Bobby Bowden 5-6. Bear Bryant 1-9 at A&M, 5-4-1 at Alabama. Pete Carroll 6-6. Woody Hayes 4-3-2. Joe Paterno 5-5. Eddie Robinson 6-6, Bob Stoops 7-5. I could go on. But, take note, I'm giving you names of icons here. These are the best of the best of the best.
But, one difference between your plant and the Tennessee football team is your success is measured against yourselves. Your plant may be a whole lot better than what it was, but may be terrible compared to other similar plants (I don't know, just posing that as an example to make a point). So, I'll use Kentucky as an example. IMO, Kentucky is as consistently competitive from year to year as I've seen during my lifetime. They're pretty good. Guess where it doesn't show up? The win-loss record. They've only had two seasons in the last 8 years where they finished more than one game above .500. So,, even though they're better, it hasn't mattered. They still aren't winning.
So, you can begin to change culture, begin to make progress, begin heading in the right direction, and still experience the unfortunate problem of losing.
Most people believe that Sam Pittman and Eliah Drinkwitz did pretty good jobs last year. They were 3-7 and 5-5 respectively.
That's the best I can answer. But, it usually takes at least a year.