I think it's due to the Tegra 3, I think Nvidia is abandoning the chip.
The chip has always sucked, Great processor speed but ancient GPU and very, very power hungry.
Not that there is nothing to blame on HTC, they should have went with the Snapdragon S4 pro with the HTC One X+.
The HOX+ came out long after the Snapdragon S4 Pro was available, it was for example present in the LG Optimus G, this would have brought better graphics and better battery life (due to the 32nm build alone).
That said, I don't really care for the updates, I think hardware is moving so much faster than the Android software, that I would have ditched this phone soon enough. A phone that gets steamy hot and battery depleted an hour of playing a game is unacceptable.
If they just could release a LG G2 with 64gb....