Botnet maybe not, but as a place to store phished creds etc., quite likely.

Services like requestbin have had a lot of trouble with this sort of thing, historically https://web.archive.org/web/20190711192140/https://github.co...

> We have discontinued the publicly hosted version of RequestBin due to ongoing abuse that made it very difficult to keep the site up reliably. Please see instructions below for setting up your own self-hosted instance.

(note, that message is old, requestbin did live on despite it, iiuc)