The Contamination of Warpspace

Over the millennia, and despite the precautions taken with enchantments and shielding, the energy in the warp, became increasingly stimulated by its exposure to the psychic emanations given off by the mortal crews and passengers of starships travelling through its domain.
Not every race was a cautious as The Old Ones and these psychic emissions seeping through poorly adjusted and maintained shields were causing strange changes within the composition of Warpspace.
Navigators and Astropaths were reporting increasingly violent eddies and storms in the energy along their routes and the warp entities which had at first been recorded as small ethereal beings were growing steadily larger and beginning to take on strange horrific forms.

It seems that the energy in the warp was using the psychic emanations from the mortals passing through it in their ships to evolve new forms that reflected the emotions to which it was being exposed. Love, hate, greed, power, jealousy, pity, and even sadness were all being used to give these new warp entities shape, form and substance, and as they grew and evolved so the mortals in the ships became more heavily influenced by them and strength of their emotional responses became greater and more extreme.
Indeed it seemed to observers that the new warp entities that were now being encountered were deliberately shaping themselves and acting in ways designed to provoke a particular emotional response from the mortals on the ships they encountered.