As discussed in the MultiCloudJ introduction, it is fairly common to use more than one cloud provider in enterprises. This can happen for many reasons, like mergers, choosing the best services from different clouds, or moving gradually from one cloud to another. Because of this, you may have compute running on Google Cloud while your data or backend systems are still on AWS.
Most enterprises do not do multi-cloud just to save money. Cross-cloud setups usually happen because of practical needs such as: