The word ‘alienation’ meaning ‘cut off from others in a mental rather than a physical sense’. Poems about isolation is a category of its own, although often related.
These poems describe disconnect. They describe how it feels to be left out rather than included. How it feels to see things in a different light than those around you. Or simple being misunderstood.
The poet has a good deal of experience with these feelings from her own life. She writes about them because she wants others to feel understood. Because she wants others, who feel what she felt, to know that they aren’t alone.
Thus, the topic has come to be one of her most common ones.