An application package is a compressed file with extra conventions. I think rpm packages are usually compressed with xz, but might use a different compression program. If I'm understanding what I'm reading correctly, rpm2cpio does some introspection to determine with extraction program to use. Maybe 7zip does the same thing, or maybe it works if the rpm was compressed with a compatible program.

So I tested around and, in fact, 7zip can not immediately decompress rpms. Sorta the same with debs, it decompresses them into an intermediary format which seems to just be a tarfile but still 7zip can't do it "recursively".