You can see the main problems with this tree are the thinness of the front gullet plate (the headplate, which fits above it and which can't be seen, is probably similar) and the small size and poor quality of the rivets which join them together, through the wood of the tree, to make the front arch rigid.
A combination of these faults allows the arch to flex, loosening the rivets (you can see the heads have lifted on some) and allowing the arch to stretch. Eventually it would have failed completely.
At least in this example the girth webs run over the top of the tree. Some examples I've seen have them tacked on underneath (scary!)
PS. The bits of half-round section wire are tails from the head nails and fall-down staples. You'll find those, and tacks, if you dismantle a quality saddle, though the head nail shafts are more commonly square-section and heavier gauge.
I'm not familiar with metals by name but the it is brittle in the cheapies, no strength to it whereas in the high end it's spring steel. Any tack used in an english saddle is blued so it doesn't rust or react with the chemicals involved in tanning leather. In the cheapies the staples rust which deteriorates both the staple and the leather which results in the staples either falling apart or falling out. What scares me is people use these for jumping. In 2001 I received and email and pics of a gal who'd bo't a pretty saddle off ebay for around $125. Of course the pretties had appealed. On her first trail ride the horn broke away from the tree and was hanging on by a flap of leather. Before she got home the tree snapped and she had to walk. Could I fix her saddle? No. I have a pic somewhere of another a gal had stripped down and sent pics. Cracks in the hollow fiberglass tree. The cinching was their version of a sam stagge rigging badly done. Cinch pressure had caused it to break. That saddle lasted only a couple of leisurely rides.