Actual thought I had in the shower!
Gelatin was originally and still often is derived from meat by-products, so wouldn’t it make more sense as a meat dish?
I looked it up, and it turns out that accounts of aspic (a savory gelatin dish) predate the earliest record of gelatin desserts by more than half a millennium!
Maybe the mid-20th-century meat Jell-O trend makes more sense than I thought
I make chicken jello (from chicken skin and bones) for my cat all the time, it only takes an hour.
That’s not pure gelatin though. It’s a mix of gelatin from the breakdown of proteins, and juices from the chicken. Great for your cat without a doubt, and absolutely worth putting in home made soups or stews, but not something you’d want to use to make a wobbly dessert! Getting pure gelatin (i.e. all broken down peptides and virtually no remaining muscle protein) takes either days of careful boiling and straining, or a controlled industrial-chemical process. Gelatin was a fancy-chef ingredient when it took days in the kitchen to produce it with relative purity, but now you can buy Jell-O powder with pocket change because we make gelatin at scale using an industrial process.