Sonos speakers actually have little computers in them that do the streaming. All you are doing with the phone or desktop Sonos app is connecting to the Sonos and telling it what to do. For example, If you tell it to stream a station from Apple Music, it will do that for an indefinite amount of time all on its own - you can turn off your phone, go on a trip, even upgrade your phone and it doesn't care because the phone really has nothing to do with the Sonos playback once it starts.
They also create a mesh network in your home and this allows more reliable signal and allows them to have different zones/rooms and/or pair with each other (eg. stereo pair, sub, 5.1 etc.).
To answer your soundbar question, one could compare that to a Sonos Playbar. With the Playbar it has an optical input so it can play audio directly from TV. Instead of Bluetooth it uses Sonos to stream music from your sources. It can also be upgraded by adding a Sonos Sub and a couple Sonos Play 1 speakers for surround. Your Sonos equipment is reusable and say, for example years from now, you don't need the surround system because now you have a dedicated home theatre and wired setup, no problem and then you can repurpose the play 1's and sub for something else and the playbar is still a good sounding speaker that can be placed in a room, if needed. Some people like using Play 1 in bathrooms or Kitchens.
I just got into Sonos and started with the Playbar and a Play 1 for another room. I am getting the sub and a couple Play 3's for other rooms.