Third party SaaS offerings that move large amounts of data are effectively forced to host in AWS.
Want a small number of high-value servers (e.g. big GPUs, etc) in your own data center or colo to use for non-availability-critical purposes integrated with the rest of your AWS stack? You’d better price in egress!
Want to gradually transition to a competing cloud? Good luck, egress will bankrupt you before you finish the transition.