The short version is that Rogen didn't think the series -- which has an impressive pedigree of then up-and-coming cast members including Rogen, James Franco and Jason Siegel, and producer/writer Judd Apatow -- should have been cancelled, and Ancier feels bad about it still, 14 years later. The back-and-forth has concerned whether notes from the network should have been followed by the producer, whether the notes were stupid, whether there was more than one, and such matters. It's been generally light-hearted, but one gets the sense that Rogen is still sort of pissed off by it. Which is sort of understandable, given how important it likely was to him at the time, though plenty of people from the show have survived well.
More to the point amid all the "Why did you make such a stupid decision cancelling Freaks and Geeks?" and "I still fee angst-ridden for cancelling Freaks and Geeks" is one tiny sentence in one of Garth Ancier's public responses, buried towards the end, which could have made this oh-so-much a shorter controversy. After a long preamble and more details, he eventually gets to the last paragraph which begins with a great deal of mea culpa hand-wringing angst, stating --
"I absolutely hated canceling this particular show. It was clear from the very beginning that Freaks and Geeks had great writing from Judd and Paul Feig, and a tremendous cast. This was an awful decision that has haunted me forever."
And then finally, after all of that and at long last -- after days of public back-and-forth between the two men, and coming at the end of this particular long explanation, he eventually writes --
"But the show was consistently NBC's least-viewed."
And the show as actually cancelled?? Oh, heaven's to Betsy. Gee, ya think?
Honestly, I love supporting craft and excellence over merely raw numbers. And sometimes you do have give extra care to certain works, and nurture them along, taking even a hit along the way. There are many examples where poorly-rated TV shows were given more time and an extra chance to succeed -- and did, some even becoming beloved classics. But...I get it wen you are not only the least-viewed, but "consistently" the least-viewed, and you were given 18 episodes, almost a full year to get an audience (rather than getting cancelled after two or three weeks as often happens), and are finally cut lose, with regret.
If few people want to see your show, you get cancelled. It's how it works. And after 14 years, it's probably time you figure that out.