in combat, everything is disposable depending on tempo. a heavy, expensive, complex belt box is not better than a disposable, cheap, simple, disposable belt box. that's the reality of combat. MG's are purposefully designed with positive feeds so that debris ingestion can be ameliorated to a degree and it is easy to clear and keep uptime on the gun because doctrine generally uses volume of fire and achieving and maintaining fire superiority as integral to winning fights.
i'm not saying it's a bad idea or bad technology, but it is not compatible with modern warfare outside of very specific contexts.