Java generics aren't the best example of how to implement generics. C# or Rust are better in this regard, which both have reified generics. Generics do solve a practical problem identified decades ago, ad-hoc code generation or void* aren't the solution. I don't think the omission of generics has any bearing on how easy writing tooling is.

You can always omit them, if you're prepared to deal with code duplication, but I think you're downplaying its significance: it is not just "maybe some" code duplication, nor is it a "a few casts". It's sometimes a deep, murky swamp you're forced to trudge in, and it's not pleasant.