Only some text can be clipped?

I’m noticing that only some types of text can be clipped from a web page. Is this true?
For example, I can clip just about anything from:

but almost nothing from:

Any insights as to what the limitations are?

The majority of this page is an iFrame, which is different website, unfortunately. The clipper won’t have access to this data.

The below is all the clipper will have access to