Silicon is indeed sensitive to light beyond 1100 nm. However, the reason CCDs cannot detect these wavelengths is somewhat complex:

A CCD operates by absorbing light and converting light energy into electrical energy. These electrons are transferred within the CCD to an output amplifier, where an electrical signal proportional to the light energy absorbed by the pixel is generated. The light energy absorbed by silicon depends on wavelength.

Blue light is highly absorbed by silicon, and most of it is actually absorbed in the multiple silicon layers on the CCD. As a result, only a small fraction of blue light is absorbed in the depletion region of the CCD, where electrons are collected by the pixels. At the other end of the visible spectrum, red and near-infrared light are also only partially absorbed. Therefore, only light that travels through a significant thickness of silicon can be absorbed to generate electrons. These electrons either drift into the CCD depletion region to be collected by the pixels, or drift elsewhere until their energy is dissipated.