Why? They can buy them from the specialists like they do other things from the Ravens, and they still take their regular testing Trials on the ground as well as engaging the other Clans and the Inner Sphere on the ground.
One thing I will note, the Sharks (turned Foxes) felt impressed enough that they got the right to produce the Morrigu and Morrigu (Laser) which they were selling to the Inner Sphere. I am not sure where they build it post-Reavings, but they got it on their way out of the Home Worlds. Then in 3083, the HAG variant was developed . . . collaboration with the Horses? Horses winning the right to produce the design themselves?
If you have never tried one out, the Morrigu are monsters though I have never tried the HAG design. Find your path, roll forward 3 hexes and kill everything. The Morrigu (Laser) is basically the Schrek IIC . . . and it has 2 tons less armor than the original.