First I wanted to get this out of the way: I am an ex-vegan. I went vegan in college for animal rights reasons, back when that was much harder than it is today, and I remained vegan for about three years before transitioning to ovo-lacto vegetarianism for another four years and then to a (mostly) whole-foods omnivorous diet after. I was a very serious vegan, checking the labels of everything I bought to make sure I was avoiding honey, lanolin, cochineal, gelatin, rennet, and seemingly hundreds of more obscure ingredients, and I never bought animal-based fabrics, like leather, silk, wool, or fur.
In fact, when I finally gave up vegetarianism, it still took me a really long time to get back into the habit of buying animal-based clothing. I still bought "vegan" shoes made of canvas or fake leather, I still avoided wool (I had convinced myself as a vegan that I was allergic to it), and I thought nothing of buying things with faux fur trim. The reason was simple: I knew why animal products were nutritionally necessary for me. I knew that sustained veganism had compromised my health. I could not--at that time--think of a good justification why "vegan" clothing was a problem.
Eventually I learned that there is, in fact, a problem: Most of the clothing marketed as "faux" or "vegan" is made out of plastic. Plastic is one of the top environmental and health hazards of our time, and plastic clothing in particular is largely made to meet the demands of ultra-fast fashion... they use plastic and especially polyester because it's extremely cheap, giving it the illusion of being disposable. While a big part of the problem is simply that people are being encouraged to replace clothing much sooner than they really need to, even a well-cared-for polyester garment that is worn for many years will inevitably wind up in a landfill to break into microplastics and poison the Earth forever after. Prioritizing your fabrics be "vegan" above anything else pretty much guarantees that you are contributing to this. Hell, if somebody is referring to their product as "vegan" without specifying what natural alternative it's made of (bamboo, leaf leather, etc.), you can pretty much just assume it's plastic.
The same mindset has leaked into the Pagan and Witch community, so there are a lot of ritual tools and especially things like tarot bags, altar clothes, ritual tools (especially statuary), ritual garb, and general Witchy accoutrements that are labeled "vegan" but made out of polyester, acrylic, PU leather, resin, or some other plastic bullshit. This is classic greenwashing. They know that the label "vegan" has a (somewhat exaggerated) reputation for being eco-friendly, they know that Pagans and Witches as a general rule want to be (and look) eco-friendly, so they slap this label on things that may not have any animal products, but nonetheless are not eco-friendly.
In many cases an animal-based item will simply be the best option. I never buy "vegan" shoes or boots anymore. The last pair of "vegan" shoes I wore crumbled into a thin layer of microplastics in the woods while I was hiking, and at that point I realized I've never had a pair of high-end "vegan" shoes last long enough to justify either the price or the plastic. While leather certainly has its own environmental impact, it is easier to repair, it lasts a long time, and when I'm finally done with it, eventually it will decompose.
I eventually developed into a pretty heavy user of animal products. To be clear: I am not saying you have to use animal products. There are vegan options that are sustainable, or at least much better than pure virgin plastic (hell, recycled plastic is a great option). These are frequently much more expensive than animal products, and their durability varies a lot, but they exist and you are certainly welcome to use them. I'm simply saying that you can't rely on the label "vegan" to determine whether or not your ritual tools, garments, and supplies are appropriately friendly to the Earth, and that the label "vegan" automatically makes a product suspect because it has been so heavily abused as a way of greenwashing plastic materials.
In addition, using animal-based materials opens up a lot of possibilities from an animistic and magical perspective. This is my own unverified personal gnosis, so you are under no obligation to accept this yourself, but I feel plastic as a material is processed to the point of being almost devoid of magical correspondences and natural spiritual essence... yes, it can develop correspondences and spiritual essence based on how it's shaped, colored, and used, but it simply isn't as effective, magically-speaking, as natural materials. All natural fabrics and materials carry the natural correspondences of the plant, animal, or other natural material they came from, which opens up a lot of possibilities for ritual garb, altar cloths, ritual tools, and so forth. Embracing animal-based materials gives you more options. One of my own projects involves making granny squares out of yarn sourced from a wide variety of wool-bearing animals--sheep, goat, yak, camel, rabbit, bison, etc.--with the goal of eventually making a ritual garment that incorporates the energies of all of them. Many of these yarns are produced in small batches by traditional herders.
I would like to maintain that, as an animist, I also believe that the treatment of an animal in life affects those energies, so you have the obligation to make the best decisions you can with that regard (and no, I don't believe you can simply cleanse animal cruelty out of animal parts with herbal smoke or whatever else). Animal products are just as easy to greenwash as plastic, after all. But being vegan is no longer a standard I hold any of my ritual tools, fabrics, or anything else for that matter to.
Happy Trails,
Wolfpeach