Why is the API key needed for bots?

Unlike the HTTP Bot API — which only requires a bot token — Irenogram directly implements the Telegram MTProto protocol. The MTProto protocol requires every client application to identify itself with an api_id and api_hash obtained from my.telegram.org.

This is not an Irenogram limitation. It is a Telegram requirement for all MTProto clients, whether they act as users or bots.