I have not used AWS and I am not sure if I understand the pricing structure, but wouldn't it cost like $30,000 per month if the server is running at 12k messages/second?

https://aws.amazon.com/api-gateway/pricing/

At this point I feel like that most AWS services are for marketing purposes. The type of people who would pay 30k a month for 12k msg/s are very few.

It's just there so you can awe developers at the breath of services AWS provides.