Why? The whole point of not showing the whole list is so that people don't only just always run the same (perceived best) missions. The whole point of storing the mission list seed would be to reduce the supply of these items, so increasing their yield (or adding the chance of getting them to other missions) would defeat the purpose of storing the seed.
The only real why would be to still have a point to running the missions.
If the low-grade mission never return the mats you want, but you are forced to run them as the only way of resetting the mission list, it seems to move the action of crafting further away from something fun to do.
Edit: Doesn't mean it would need to return the same amount of materials as the higher grade missions, or even that it would have the same crit rate. But for there to be no chance whatsoever to get the materials you're looking for, but you have to run them anyways ...
Edit Edit: I just re-read your post and realized I overlooked this:
... The whole point of storing the mission list seed would be to reduce the supply of these items ...
Is that the reason why you're suggesting to keep the seed the same? To reduce the supply of items?