I once had a saddle that looked like that one.
It got that way by being saturated with rain water and ridden while wet. Ridden wet, the leather stretched and sagged.
I tried to repair the leather with various treatments like Proofhide and Neat's foot oil. Nothing could "unstretch" the leather.
When I tried tensioning the bolt in the nose, it raised a pronounced ridge from the nose to the tail just like the saddle, above.
That saddle is shot. They polished it to make it look nice but it is still shot. Look for another. It's as simple as that.