The wonders of gelatin: redux

I know I’ve been on this subject before but I really don’t understand. Why isn’t this used on 90% of FX prosthetics? I foam it to act like a cross between silicone and foam latex, or use straight as an excellent silicone replacement and you can throw literally anything into it and it won’t impede its properties. It can be transparent, translucent or opaque. Gelatin is painted with anything unlike silicone. It’s the cheapest material around and best of all reusable. The only downsides are it’s a bit heavier than foam latex, water soluble (although with enough zinc oxide that isn’t an issue) and will melt in extreme heat. What gives?