I used to think that way myself. Then I had both anklets fail at once just momements after giving them a visual inspection. They did show some wear, but they looked like they were still very serviceable. They werent even unsually stiff. Luckily, this happened in the house just after I put my old goshawk Angel on the screen perch. She had a habbit of giving a good solid bate just after being placed on the screen perch, and both of them gave way when she did this. The funny thing about it was that she was so surprised by the event that she fell out of the air.
I love leather. Love working with it, love looking at it, love the smell of it, love the feel of it.
But it has a lot of disadvantages. Especially if you have a goshawk that loves to soak her feet in the tub (most of them do I believe) and/or live in a climate hostile to leather, like say a rainforest.
Synthetic materials fail as well, but I am going on over 10 years of service life for some of my leashes, and they look like they did the day they were made (with a bit of grime thrown in for character).