Cargo is really simple, which is great, but also limiting. Maven is much more complex, but for good reason - there's use cases, especially around multi-artifact projects and version sharing, where cargo would require either some glue or you run into some interesting edge cases. Usually, Rust isn't used for the kinds of big, wacky projects with a million dependencies that companies write in Java/Kotlin, so those kinds of use cases are considered more unusual.
Gradle, in my opinion, makes itself complex because it's all code, is very brittle, and several of its features just don't work right and require workarounds. When it works, it builds fast and it works well, but getting it to work, and how often you have to get it to work again...not worth it.
Lots of little quality of life things. For instance, in Kotlin types can be marked nullable or not. When you are passing a potential null into a non-nullable argument, the compiler raises an error.
But if you had already checked earlier in scope whether or not the value was null, the compiler remembers that the value is guaranteed not to be null and won't blow up.
Same for other typechecks. Once you have asserted that a value is a given type, you don't need to cast it everywhere else. The compiler will remember.