I believe Google Cloud was launched after AWS so a head start helps for one.
AWS also has a free tier, it’s like giving the first hit of ecstasy to someone free. Why not use this free server. Then that server needs to expand and you make plans and youre hooked and know the AWS cloud better than Google.
Google Cloud offers a credit of $300 right now to try and get you involved but its not the same as a free tier of service. Once the $300 is gone its always going to cost you whereas you can downgrade