The company I worked for in the early 80’s was in the market for a CAD system, and they all had constraint systems in the UI, and showed them in the demos.

CAD people got this a long time ago, but, unfortunately, HTML people never did. Layout is a 2D constraint problem, but HTML/CSS approaches it as a procedural problem, partly because early browsers were so compute and bandwidth constrained.

CAD is great at parametric design, which gets significantly more complicated when the viewport changes shape.

Taking a procedural approach instead of solving constraints is necessary for folks to stay sane when they're trying to get the same website to work on phones and desktops.