..because we like the taste of meat.
Vegans are by no means concerned only on food because veganism means not only to stop consuming meat, fish, poultry, dairy products, and eggs, it rejects the slaugther and exploitation of any creature for any reason.

Clothing: Reject Fur, Leather, Wool, Silk, Reptile Skin, …
Chapter 1: The fashion victims
Solely for the purpose of fashion approximately 40 million animals are killed every year. This figure does not include the number of animals processed for leather and wool products, since they are more a byproduct of animal use for food.
Three-quarter of the 40 million animals including minks, foxes, chinchillas, and raccoon dogs are raised and killed on so-called “factory farms”. Most of you know under which horrible conditions in small wire cages these animals have to live to maintain maximum profitability. These confinements cause often ulcers and other physical disorders. Almost all animals develop various behavioral disorders and start to self-mutilate in this environment. Finally, after a short life of about one year they are killed by electrocution, gassing, or neck breaking.
It is also known that factory farms does have a devastating impact on the environment due to enormous production of soil, water, and air polluting waste.
The remaining quarter mostly consists of trapped animals which suffer to death by dehydration and blood loss or will be killed by shooting, stomping, or clubbing. Not included in this figure are trapped non-target “waste” animals which are estimated to be about ten times as much [1]. Taking into account that ten to hundred pelts are needed to produce one coat, a truly insane number of animals have to die cruelly for the sake of fashion clothing.
Due to the fact that cotton and synthetics provide proven alternatives, nobody can seriously maintain that the use of animals for clothing is necessary.
If it is wrong to inflict unnecessary pain and suffering on sentient beings, then we have a moral and legal obligation to reject clothing made of animals.

You have the power to decide.

[1] Humane Society International (HSI) http://www.hsi.org