Rails has several pain-points for more complex web applicatoins that frameworks like Hanami and Trailblazer attempt to address. By addressing theses issues your business logic is better isolated from the framework details/implementation, clearer responsibilities, easier reasoning about, cleaner code, creates opportunity for easy further abstraction when necessary, allows for simpler testing, etc.
Better file structure/autoloading that allows grouping of domain concerns under a single folder structure
Solutions: use custom autoload_paths/eager_load_paths in an initializer?