Most large companies do at least some elements of multicloud. This may be as simple as doing ETL in AWS and then pushing the data over to BigQuery for dashboarding, it might be using all AWS and also Office365, it might be building applications which part run against Dynamo and part run against Cloud Spanner.
It's also the case that the applications you run each year have some turnover rate. Maybe you're running Jira this year, maybe you're switching to Asana in a couple of years. Maybe over a 5 year period you're moving from Teradata to Snowflake. Which cloud env do you deploy Snowflake to?
Your negotiating power is then in the momentum of change. If GCP is working better for you than AWS right now, send your new spend to GCP where possible and where stuff is rotating out, move the new stuff to GCP. If you just got a good deal from Azure, start moving in that direction.
This is one of the 'big company vs small company' things, by the way - it doesn't make as much sense for a 100 person startup. But FedEx are a 300k employee juggernaut who spend $75B each year servicing $100B of revenue. They'll have a lot of tech in use.
Your negotiating power is then in the momentum of change. If GCP is working better for you than AWS right now, send your new spend to GCP where possible and where stuff is rotating out, move the new stuff to GCP. If you just got a good deal from Azure, start moving in that direction.
This is one of the 'big company vs small company' things, by the way - it doesn't make as much sense for a 100 person startup. But FedEx are a 300k employee juggernaut who spend $75B each year servicing $100B of revenue. They'll have a lot of tech in use.