Because "addressing" the concerns would make Rust a worse language.

1. Removing structs and interfaces (in favor of what? Java-style classes and interfaces?) would make Rust more verbose, less of a systems language, and slower at runtime due to the indirect dispatch.

2. Changing the keyword "enum" to something else is a cosmetic change which would make as many users unhappy as it made happy. (We know, because we solicited feedback on the keyword before selecting it!)

3. I've addressed error handling in the sibling comment. There's basically no other way to do it that would be in line with Rust's goals as a systems language.

4. Rust would be a worse language if it lacked closures. Closure support is a basic feature in a modern language.