They won't work because the Xbox One is X86 architecture, while the Xbox 360 is PPC (PowerPC). Quite simply these two machines don't speak the same language. The PS3 is also PPC based, while the PS4 is X86. PS3 discs won't work in the PS4 for exactly
the same reason that it too is X86.
Software emulation was the solution for running original Xbox games on the Xbox 360. Unfortunately, the Xbox One's CPU won't be up to the task of emulating the Xbox 360, at least not at anywhere near full speed. The only other option would have been to include
the Xbox 360's hardware inside the Xbox One, but this would have increased the size of the machine, heat, the overall complexity of the motherboard, and the price.
The original PS3 models could play PS2 games because they included the PS2's chipset into the system motherboard. However in later models, Sony removed the 'Emotion Engine' CPU to reduce costs, which impacted on PS2 backwards compatibility. Finally in 2009,
Sony removed the 'Graphics Synthesiser' GPU, completely removing all PS2 BC.
In case you were wondering, the Wii U has the same type of processor architecture to the original Wii (PowerPC) and a more powerful AMD graphics card. This is the reason why all Wii games work on the Wii U.