Question 'Select Material' dialog doesn't rebuild material previews?

I was wondering if there was something I had to do in order to get Material previews to build properly in the Select Material dialog. I do see previews on a small number of materials, but usually this is what I see:



It seems that if I click on a material in the Project view, such that its preview is generated within the Inspector pane, that preview is now viewable in the Select Material dialog:



But it seems the Select Material dialog itself doesn't trigger the generation of previews. Is that a bug? Or is that to prevent a huge performance drop as potentially hundreds of previews need to be generated? This is under HDRP 7.5.1.