>But you can also have your jeans tailor made.

The result of this process would vary widely based on what you call "jeans". If it's any denim pants then sure, you can just use the same cut as suit trousers and get well fit "jeans". Some people call "jeans" only pants cut in a fashion similar to Levi's 501. Those don't have darts or pleats so even if a taylor hand stitched such a cut it simply doesn't have as many "knobs" to fit one's legs shape as well as suit trousers.

Same principle applies to any other garment. They are all made from flat pieces of fabric stitched together. The fewer pieces and fewer stitches there are, the harder it is to fit to the body shape.