The direct cost is the easy part. The more insidious part is that you're now cultivating a growing staff of technologists whose careers depend on doing things the AWS way, getting AWS certified to ensure they build your systems the AWS Well Architected Way instead of thinking themselves, and can upsell you on AWS lock-in solutions using AWS provided soundbites and sales arguments.
("Shall we make the app very resilient to failure? Yes running on multiple regions makes the AWS bill bigger but you'll get much fewer outages, look at all this technobabble that proves it")
And of course AWS lock-in services are priced to look cheaper compared to their overpricing of standard stuff[1] - if you just spend the engineering effort and IaC coding effort to move onto them, this "savings" can be put to more AWS cloud engineering effort which again makes your cloud eng org bigger and more important.
[1] (For example implementing your app off containers to Lambda, or the db off PostgreSQL to DynamoDB etc)
("Shall we make the app very resilient to failure? Yes running on multiple regions makes the AWS bill bigger but you'll get much fewer outages, look at all this technobabble that proves it")
And of course AWS lock-in services are priced to look cheaper compared to their overpricing of standard stuff[1] - if you just spend the engineering effort and IaC coding effort to move onto them, this "savings" can be put to more AWS cloud engineering effort which again makes your cloud eng org bigger and more important.
[1] (For example implementing your app off containers to Lambda, or the db off PostgreSQL to DynamoDB etc)