HOW DOES THAT MAKE ANY SENSE?!?!
Like it or not, we're stuck on Von Neumann architecture, and as a result, data can be treated as code and vice-versa. The consequence of this is that, under certain circumstances, data can be carefully crafted to act as code, and can be executed in an unforeseen context. As a software engineer, it is your job to take precautions when developing software. Precautions that prevent this execution. Security people do the best they can to make it easy to develop safely, but all of that is useless if the developers ignore it. And, because security vulnerabilities are a manipulation of context-and-program-specific control flow, there's not a way to encapsulate all security measures in a way that is transparent. It's just not possible. Only developers know the specifics of their software, and only developers can protect certain edge cases. If you assert otherwise, you have a fundamental misunderstanding of the systems that you work with, and you need to re-evaluate your education before continuing to work in the industry (assuming you do). This isn't an opinion. This is a fact.
Lastly, us "security experts" do contribute to our field. Security is one of the hard problems in computer science - far harder than whatever you're doing that lets you "not think about databases, deployment, testing, scaling" - and there's a lot of solutions that have been engineered to deal with software that has been created by people like you. There's static code analysis tools, which can detect bugs in code before it is even compiled. There's memory analyzers that can detect dozens of different classes of memory-related bugs by just watching your software run. There's memory allocators and garbage collectors that can prevent issues with use-after-free and other heap-related exploitation bugs at run-time. There's data execution prevention and buffer execution prevention that, at run-time, help prevent code from being executed from data pages. There's EMET and other real-time exploit detection tools that exist outside of your software and can still prevent exploitation. That's not even an exhaustive list. There are literally hundreds of tools out there that make finding and fixing security bugs easy, but those tools can't patch your code for you. That's why there are consultants, code auditors, and penetration-testers that can give advice on how to fix bugs, find bugs where automated tools fail, and even coach developers into writing more secure code; because having smart, security aware developers is one of the major ways to defend against security bugs.