Earplugs only protect the individual wearing them. A suppressor, like a car muffler, helps everyone within earshot.
Additionally, plugs or muffs impair the user's awareness of quiet sounds, an important consideration during some forms of hunting and particularly indoor self-defense.
This factor can be mitigated with active noise-canceling muffs, but these are seldom practical for self-defense. Furthermore, the only active muffs I've ever used that IMHO were truly "invisible" in terms of allowing the user to hear very quiet sounds was a $1,000 Bose aviation headset- NOT a practical investment for most shooters, and not comparable to a "can" that would realistically cost ~$50 if it wasn't for the NFA nonsense.