@slavmaster Suspension would improve performance in rapidly crossing extreme terrain for sure. You need that for transporting men and material, but that's not what this is for. It's primary role is as an earth mover for road building and engineering works like trench digging. In those roles having full suspension actually works against you. With fixed axles, any forces from your attachments like blades, buckets, ect., can pass straight through the chassis and back into the ground. If you're fully suspended, the suspension dampens the energy transfer lowering the amount of force you can exert with the attached tool. You don't get 100% energy transfer until the suspension fully compresses. If you need a clearer example, try lifting weights while standing on a stack of mattresses. See how much power those nice comfy springs suck out of your legs.
Stability is another part. You need your center of gravity as stable as possible for any kind of heavy lifting. Suspension means the chassis can sway and roll at whatever angle it wants, throwing your center of gravity all over the place. That's only useful if you want to end up in a "forklift fail" compilation video. Outriggers can solve this somewhat, until you have to lift and move at the same time.
Sorry if this is a bit wordy. I work with industrial power equipment and have seen WAY too many training videos at this point...