They have purposely disabled being able to select text (outside of the SVG graphics) by literally doing this in CSS:

    * {
        user-select: none;
    }

The user-select: none; is intended for places where interaction with an element (e.g., drag and drop, clicking, sliding) is required and text selection should not occur. You might use it discretely on a HTML button.

Blanket banning of text selection is a habit I've seen with developers who live in a touchscreen-heavy bubble, and who feel that users have no reason to select text at all unless explicitly enabled by the developer.

> As citizens of the technology era, there is an undeniable need for optimal clarity in our writing.

There, I copied that quote from their website (by disabling the relevant CSS); one example of a totally valid reason for wanting to select text.