Silk is a protein. That means it's encoded by DNA. Kevlar is ultimately a chemical - not dissimilar from a complicated sugar. To make complicated property ch

Silk is a protein. That means it's encoded by DNA. Kevlar is ultimately a chemical - not dissimilar from a complicated sugar. To make complicated property changes to a small molecule requires significant R&D and is ultimately not very predictable. To make complicated property changes to a protein is as straightforward as flipping a bit in the DNA that encodes the protein. That can be done for literally $100, overnight. And though still a bit of a messy problem, it's actually significantly easier to predict what will happen when you alter the protein. Further, we have a catalog of amazing material properties pre-made for us (see life - organisms - geckos, flowers, butterflies, birds, etc.) which can be incorporated into the silk protein's DNA at again, near trivial cost. Many will not work, but many will. Tldr: silk is amenable to synthetic biology, older textiles such as Kevlar are products of old-school chemistry and have a limited innovative potential as compared to a genetically encoded material.