Why is the caterpillar’s question not an encouraging opening for a conversation?

Caterpillar is full of questions, but his repeated use of the question, "Who are you?" is anything but welcoming. Caterpillar wants answers to his question, and Alice is unable to give them. His demeanor frustrates her.

“Who are you?” said the Caterpillar.

This was not an encouraging opening for a conversation. Alice replied, rather shyly, “I—I hardly know, sir, just at present—at least I know who I was when I got up this morning, but I think I must have been changed several times since then.”