Some (large) companies have automated processes where you’re forced to book travel arrangements through intranet portals with a limited choice of suppliers.
I've worked for and know many people that work for very large (F500ish) companies, as well as the large consulting companies (Deloitte, Pwc, Accenture, etc), and booking your own flights/hotel is standard practice at all of the consulting companies and most of the others.
Interesting. I’ve never heard of a corporate department that books your travel. Sounds like a hassle. Any company I’ve been at, big or small, just has their policy parameters enforced by third party booking tools.