I have definitely heard of negotiated travel deals where the company gets some percentage of the spend back. So for instance a Delta flight might not be cheaper

I have definitely heard of negotiated travel deals where the company gets some percentage of the spend back. So for instance a Delta flight might not be cheaper than United on the ticket booking site, but it ends up costing the company less. OTOH this was a Fortune 100 company with high travel spend so they had quite a bit of leverage.