See belt squats are a bit different. On leg presses with 1,500lbs or whatever ain't no training partner helping you do forced reps. Even with one on each side it's hard to get that type of load off a guy who fails. Nevermind for several forced reps, ain't happening. What they do, and you can see this on pros' videos, is that the spotters help a bit when the reps get hard, before they would have failed. Someone like Jordan Peters probably fails a lot but he's an anomaly. I always cringe when I've seen pros leg presses at Gold's Venice, tons of plates and no safety mechanism to bail if something snaps. It can happen at any point, long before failure.