Leather is one of those textiles that is difficult to mimic in a way that’s sustainable. There is an ineffable something about real leather that can’t be compared to anything else, but it’s hard to justify killing an animal just so that you can have a nice purse.
Plus, even when you set aside the ethics of animal products, real leather is terrible for the environment.
It’s basically plastic and we’re all becoming more and more aware of how bad the manufacture and disposal of petroleum-based products is for the environment.
For weather-proofing and durability, it’s hard to beat leather, so more and more people are trying to find a better solution.