The same way you don't write, maintain, and extend a thousand lines of IAM policies and roles, network ACLs, and launch configs in CloudFormation templates when you can have a specialist do it for you.
That said, I can understand the desire to gatekeep as someone in an operations role. Our role (as a generalization) is about scalibility, reliability, and availability. Developers (as a generalization) tend to care more about velocity, blue sky projects, and minimizing effort for the outcome.
Maintaining a balance between those two mindsets requires a lot of skill.
The same with devops. I know the devops folks enjoy having sql upgrade scripts and build and deployment scripts (currently yml or CF templates) handed to them that have already been tested in a Dev environment.
Also, if the developer isn’t knowledgeable about scaleability for instance, no matter how many servers you add behind a load balancer, if they store session state in memory instead of using something like ElastiCache, there is nothing you can do operationally (well technically you can have sticky sessions but that’s gross).
Even if the developer doesn’t do every part of the stack, they still have to know how to.
I don’t want to have to be the only one, but I like having both the knowledge and the access not to have to wait on someone else. I gave up a job as an architect with so much red tape I couldn’t get anything done at a large company to be a senior developer at a small company where from day one I was given admin access to AWS (yes I have the skill set and the certifications for what they are worth).