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.
Some estimates say that as many as a billion animals per year are turned into leather products, but it's impossible to know how many are a byproduct of the meat industry or simply killed for their skin.
Plus, even when you set aside the ethics of animal products, real leather is terrible for the environment.