The "Imperium" forces invaded planets and fought ground wars because the T'au could build orbital shipyards from the ground at short notice.
As a result, countless worlds kept demonstrating their launch vehicle capabilities and their ability to assemble shipyards in space.
What if they didn't have that many shipyards? Fake them!
The "Imperium" had no way of knowing whether their shipyards were real. It wasn't as though they were launching and assembling them right in front of the enemy.
World after world beyond Vior'la began an all-out campaign of fakery.
The ground war on Vior'la continued. Once the smaller areas had been cleared and most of the easily transported warship debris used up, only a handful of major settlements remained unconquered.
They were something like human hive cities, though nowhere near as large. The T'au population was small.
But their warehouses, weapons, and equipment were all there.
Evan wasn't particularly keen on smashing them with warship debris, either.
So he turned and opened a comms link to Annos.
"Annos, how's Mororis doing?"
"The Chief Librarian is in good condition, but I wouldn't recommend deploying him."
?
"Why? He's getting old. Let him get some exercise."
"Well... it's just... he seems a little addicted to new technology. I haven't installed any of it for him yet. I'm worried that if he comes out this time, he'll beat me up first..."
"..."
"Old technology works too. Give him more weapons and let him shoot everything in sight. That should improve his mood."
"But... the replacement legs I ordered from the Forge World after he lost his last pair in battle haven't arrived yet..."
"Don't you have spares?"
"I do, but that set is an eight-legged spider chassis for crossing difficult terrain. We retired it after installing the antigravity system..."
"Who cares?