They did. This was literally their defense in Epic lawsuit.
Summarized Apple lawyers said: "We can't offer alternative stores because they would be full of scams which would be bad for users. Our store is curated and safe for users.".
For over a decade, the App Store has proved to be a safe and trusted place to discover and download apps....And a big part of those experiences is ensuring that the apps we offer are held to the highest standards for privacy, security, and content."
The page then says this about security:
"Security for every app.
At every level.
We ensure that apps come from known sources, are free of known malware, and haven’t been tampered with at the time of installation or launch."
And this about trust:
"Apps must adhere to our guidelines.
When you download an app, it should work as promised. Which is why human App Reviewers ensure that the apps on the App Store adhere to our strict app review standards. Our App Store Review Guidelines require apps to be safe, provide a good user experience, comply with our privacy rules, secure devices from malware and threats, and use approved business models."*
Yeah. The man who lost his life savings due to malicious iOS software bearing Apple's signature of approval should directly cite this as evidence that Apple is responsible for his losses. Apple should pay back every last penny, his lawyers and more for good measure.
Summarized Apple lawyers said: "We can't offer alternative stores because they would be full of scams which would be bad for users. Our store is curated and safe for users.".