Wavenumber range reversed in IR spectroscopy
Sorry, I can't comment yet. I thought I'd add a historical perspective, which I don't know if it is true, but it occurred to me as a good reason for why this might be the case.

UV should historically preceed IR. In UV, the energies axis has been historically reported in wavelength (nm), which is inversely proportional to energy, meaning you have high energies on the left and low energies on the right.
It might be that for consistence with UV, the wavenumber axis has been reversed so to have higher energies on the left.

This is highly speculative, though.