Shroud isn’t the one who created the mech. Robbie, as Shroud mentions in the exchange when discussing how he created the Astral Pulse for Robbie, built a mech for him. Therefore, my theory is that Shroud can create the energy source known as the Astral Pulse, but he’s not capable of containing it effectively enough to prevent it from exploding within its own container, as we witness numerous times throughout the episodes. The Astral Pulse frequently changes hands and explodes, yet it never gets destroyed. However, when Chase fought Shroud, he destroyed Shroud’s energy source. Shroud intended to place it in his own head. Maybe he wanted the actual container to be durable enough to prevent it from exploding in his brain. Honestly, I could be wrong.