A carrier is not a container. That's the whole point.
Swings, bouncers, rockers: those are containers. Baby goes in, you step away, baby sits. A carrier is the opposite. Your baby is with you, moving when you move, hearing what you hear, engaged with the world while you get things done. That's hands-free and active stimulation at the same time.
It also means you're not tied to a stroller. Airports, farmers markets, cobblestone streets, bathrooms where the door opens the wrong way: a carrier goes everywhere a stroller turns into a negotiation.