Given Ruby's lackluster type system, the amount of assumptions a compiler can take is significantly reduced. Moreover, analyzing that at a simple IR level would prevent it from understanding of what is actually referenced vs what isn't without making compile times take eternity and performing complex flow analysis with simulation.
Even with a good type system, a trimmer/linker has to be enlightened of many special idioms and patterns and perform flow analysis, and in the case of dynamically typed languages or languages with reflection - to analyze reachability of reflectable members and trim otherwise spaceous metadata. It took significant amount of work in .NET's ILLink in order for it to be able to produce as compact binaries/libraries as it does today with .NET's AOT build target, and it still required a degree of metdata compression and dehydration of pointer-rich data structures (something which, funnily enough, Go doesn't do, resulting in worse binary size).
Even with a good type system, a trimmer/linker has to be enlightened of many special idioms and patterns and perform flow analysis, and in the case of dynamically typed languages or languages with reflection - to analyze reachability of reflectable members and trim otherwise spaceous metadata. It took significant amount of work in .NET's ILLink in order for it to be able to produce as compact binaries/libraries as it does today with .NET's AOT build target, and it still required a degree of metdata compression and dehydration of pointer-rich data structures (something which, funnily enough, Go doesn't do, resulting in worse binary size).