Recommended reading:

• https://docs.unity3d.com/Manual/SL-MultipleProgramVariants.html

Keywords will only take effect if a shader variant is present in the build with that exact set of keywords enabled.

If you set the keywords:

cmd.EnableShaderKeyword("_KEYWORD1");
cmd.EnableShaderKeyword("_KEYWORD2");
cmd.EnableShaderKeyword("_KEYWORD3");

But the only shaders present in the build (after stripping) are:

_KEYWORD1 _KEYWORD2
_KEYWORD2 _KEYWORD3

Unity will apply a fallback mechanism¹⁾ to select a variant shader with the closest set of keywords.

Sometimes it's useful to debug which shader variants and keywords are actually being included into a build. The “Compiled Code” drop-down in the shader inspector has a button to show the variants included in a build, and more importantly, why. Some keywords are always included in a build, globally, and some are only included if a scene uses a material with those keywords.