Can't enable Main Light Cast Shadows in scripting

In the editor, when configuring the LightweightRenderPipelineAsset I can set "Lighting -> Main Light -> Cast Shadows" to Checked / Unchecked, but in scripting, the corresponding property "
supportsMainLightShadows"
is read-only ( has a getter without a setter). Why is that, am I missing something?

I also can't do this when changing the pipeline asset using this code:

Code (CSharp):

1. GraphicsSettings.renderPipelineAsset = asset

If the pipeline asset the game started with didn't have "Lighting -> Main Light -> Cash Shadows" checked, that switching to a different pipeline asset where it is checked doesn't enable the Main Light shadows.
I was hoping that enabling it manually in script would help, but as it's read-only I can't do that as well.

Edit:
Unity: 2019.2.10f1
LWRP: 6.9.2