Maybe no one uses Liquid because
  • it's trust model is worse
  • there is basically no tooling or software support because it is seem as a Blockstream thing, not a community thing
  • it doesn't actually provide privacy out-of-the-box, you need someone to host a coinjoin pool inside and there are none -- whereas the zSide sidechain would automatically be that perfect ongoing coinjoin with no overhead, cheap fees and great UX
  • because you have to do KYC on an exchange to withdraw