It's not a case of not being worth fixing, it's one of even having the money to bother.
Whether you like or loathe Phil Fish, the creator of Fez there seems to be a consensus that the game itself is well worth playing. Of course many games these days aren't perfect at launch, and thanks to the magic of being connected to the Internet there are ways of ironing out those last few kinks: namely patches. Fez is no exception to this phenomenon, but there is something that has set it apart from the crowd in that regard, and not in a good way.
Basically the long and short of it is that roughly a month ago the patch for Fez was released, and what ended up happening is that even though it fixed some of the issues like the infinite death loops that were present in the first version of the game, it also had a rather nasty side effect of causing the game to see some of its save files as corrupted, which meant that people lost the entirety of their progress.
Now, there's not really anything terribly surprising about a patch breaking other aspects of the game. It's not something that anyone wants to happen, but it does (my knowledge in this regard comes from the multiple fixes that have been released surrounding Binding of Isaac: The Wrath of the Lamb expansion), but that's something that generally gets fixed as quickly as possible. That's why it was strange that aside from an admission that the patch was causing problems that there was no real fix or solution forthcoming.
Fastforward to now and we might finally have a reason, although some people probably won't really like or accept it. Apparently it would simply be too expensive to make another patch. Basically, in the article on Giant Bomb the following came to light:
Two, a number of issues post-release prompted Polytron to work on a
patch. Releasing a patch on XBLA costs $40,000, according to Fish (Double Fine’s Tim Schafer has separately mentioned this figure).
Microsoft gave Polytron a pass on the first patch, but when the patch
was approved by Microsoft certification, released to the masses and
caused a small number of users to lose their saved progress, Microsoft
pulled the patch.
A follow-up patch will now cost Polytron $40,000. That patch is not yet released.
this whole certification process that Microsoft has, which is in place
to ensure there’s a certain level of quality in the games,” he said.
“They don’t want games to be constantly patched all the time, and I
understand the reasoning for that, but god damnit, it takes forever, it
costs a fortune--you have to pay them for it--and it doesn’t work.”
Forty-thousand dollars to release a patch that will help make a game run better just seems, well, ludicrous would be the term that springs to the front of my mind at least. I know that it does cost Microsoft some money, but you'd think that something that allows the game to be played with less errors and possible frustration on the part of players means that it should be pushed out with minimal red tape and bullshit. Instead we get this kind of problem.
It really is a somewhat sad commentary, but I guess it's also not surprising. Fez probably has made Fish and his team a decent amount of coin, but nowhere near enough to afford that kind of price per patch, especially if this patch doesn't correct the problems and they have to roll out yet another one. Perhaps it's the inevitable price of playing in the big leagues, but that doesn't stop it from feeling more than a little rotten.