Honestly I don’t see why networks seem to keep resurrecting it but in doing so removing the core elements of what made it Big Brother and dumbing down what’s left.
The short answer is: Because they are stupid.
That answer is oozing with arrogance, but it is the truth (and it's not like they look at us differently). They are in for the money, but they lack the passion for the show. They see that there is an extremely engaged audience, but they are not engaged with that audience, they don't understand that audience and - most importantly - they don't understand the show and in the worst case, don't even care about the show and are only interested in filling TV time.
I'm sure that I've written about before and while it's not BBAU, it's the best example for that mentioned approach: When Germany brought back the civilian version two years ago, they wanted it to be big. They had a press conference and all the higher-ups at the company showed up for the press conference. People that wouldn't even show up for the yearly Celebrity Big Brother press conferences. And they've done such a pathetic job explaining why somebody should watch that show. It became so obvious that none of them will actually watch the show. They've said the most generic things about the show like how it's the original or how it's authentic.
And I think that's true for many countries. They see Big Brother as "cameras filming people in a house and an invisible voice talks to them once in a while and that invisible voice is what sets it apart from other reality shows". And from that point onwards, it's where things go wrong, because the show is so much more than that. Big Brother
Part of the issue is also, that's it's not just TV execs but also execs at Banijay. One of the cool things about Big Brother, for me, has always been how different it looked everywhere. And Banijay is going around and telling people: There is not just one Big Brother, Big Brother can be anything you want it to be. But those two things are not the same. Big Brother might look and slightly work differently everywhere, but in it's core it was the same. It's not true anymore today. Big Brother used to inspire other shows. These days, it's mainly the network's answer to other shows.
And that might work well for Banijay when they try to sell the show. But it's not the key to building a healthy franchise. And Banijay will never admit it, but the Big Brother brand is not in as good of a shape as they think. So many of the current franchises rely on celebrities these days, even in the civilian version. Banijay won't mind, because of money in the short term. I'm sure that they will mind later though.
I think you've said that you worked in production or something before, I think you've seen decisions that were motivated by financial reasons in your job, too. I have a friend that used to work in TV production. She was involved in producing a magazine-type of show for a channel and that was quite successful. They treated her as the queen of daytime. But then somebody did the maths and said that if they switch to sitcom re-runs, they might have less viewers and get less ad-revenue but save a lot of money because re-runs are cheaper... and they calculated how much the ratings could drop and would realistically drop and decided that they're better of with re-runs even though they are less successful. Because money was more important in the short-term. They might regret the decision these days when people would rather watch re-runs on Netflix.
I could rant about it for ages. And it all comes down to: They only see the money and are stupid.