Home gym systems are different from Smith machines because they combine several exercise stations, while Smith machines center on a guided bar path. A home gym system may include presses, pulleys, leg stations, benches, and cable points. A Smith machine is built around a bar that travels on rails.
The practical difference is broad station coverage versus guided barbell-style lifting. Home gym systems make sense when the user wants one machine for several strength movements. Smith machines make sense when the user wants a controlled bar path for squats, presses, rows, and related lifts.