Why isn't the De-Broglie wavelength of massive particles redshifted in an expanding universe

The de Broglie wavelength of a massive particle is redshifted in an expanding universe.

The de Broglie wavelength is given by:

$$ \lambda = \frac{h}{p} $$

so a red shift of the de Broglie wavelength simply means that the momentum is decreasing, which for a massive particle means that its velocity relative to us is decreasing.

And that is exactly what we see. Suppose someone on a distant galaxy fires a particle towards us with an initial velocity (relative to us) of $v$. As the particle crosses the space towards us the space expands under its feet so the particle slows down. We would see the particle slow down and in the absence of dark energy eventually come to a halt - in the presence of dark energy the particle can reverse direction and then accelerate away from us.

The result is that we observe the de Broglie wavelength of the particle to increase as the universe expands.