If AWS unilaterally cut egress fees 100x, then a few things might happen:
GCP and Azure customers might migrate to AWS or have very serious phone calls with their account reps. (Hmm, GCP customers might be unable to reach an account rep.)
Third party providers, who are currently stuck in AWS, GCP and Azure because their customers can’t afford egress if they move out, will consider alternative hosting. This is IMO a big one, but it has nothing to do with whether GCP and Azure play along.
Some customers might shut down their colocated systems and move into AWS.
Why is being first a problem?