Because a saddle is like a hammock and not a hard chair. It's about spreading the load. When all the pressure is on a strap, you will feel it. The more straps, the more the load is spread. Material between the straps distributes weight. Adjustments on the bridge loops distributes the weight from the top strap to the bottom strap or vice versa. Cordura stretches less than mesh, distributing the weight better but its bulkier. It's all trade offs to distribute the weight while hanging on bridge loops. Hammock style saddles have no strap and distribute the weight the most evenly, but are lacking the structural support needed for fall arrest. Every company and DIYer tries to do this in their own way. All saddles, after sitting on a strap for an amount of time, will have to be readjusted to move the pressure to a new spot on your underside. Some you can sit longer than others before adjusting. Some limit you too adjustments by design. Some have too much adjustment with too much fiddle factor. Lots going on here. Thats why we have so many different designs. The more designs the better to find one to fit our individual needs. At least until they solve the gravity problem.