They also can't really damage Adamantium... and armor made of Adamantium is notably weaker than Tau armor made from Iridium. 40K won't win the technobabble war.I mean, the amount of damage it can take and how the Imperium can't really damage it.
The people who consider prayer a part of repairing toasters have tried. The people who can't re-engineer their own toasters and instead need to scour the galaxy for an ancient schematic for a toaster, because they have no technical skills that would let them dismantle their toaster and troubleshoot it or replace the broken part have tried. Those people certainly can't design their own toasters, only replicate ancient toasters schematics they find in some ancient lost database. Those guys have tried.Imperium have tried these things though.
Remember, they have probably tried a scientific route when it comes to stopping certain things.
Also remember a chaos God is in charge of plagues
The Federation has not tried. Homer Simpson being unable to solve a technical problem doesn't mean Tony Stark can't solve it.