Because you never interact with a label directly. There is no hover, no focus, no pressed - you interact with the control it names, and the label follows. Disabled is the one state it needs, and it is 50% opacity rather than a different colour.
When do I use this instead of Field?
The source is direct: for a form field use Field, which brings its own label, description and error handling. Reach for the standalone Label when there is nothing to describe and nothing to validate - a checkbox row, a single input, a control whose own label slot is not what you want.
What is bound to tokens?
More than usual. As well as base.foreground for the colour, it binds text.sm.font-size and font-weight.medium, so a change to the type scale reaches it without anyone opening the component. Most of the kit binds only colour.