Home audio was strictly a single-speaker pursuit from the dawn of recorded sound through the late 1950s, when stereo changed the way we listen to music. Multichannel home theater's popularity peaked in the late 1990s, but starting with iPods and sound-bar speakers, mono was back in style. More recently sales of battery-powered, mono Bluetooth speakers started to take off. While these lo-fi systems may contain stereo pairs of drivers, the speakers are so small that stereo separation is nonexistent. The better home theater sound-bar speakers can generate wide and spacious imaging, but no 'bar can match the sound of stereo speakers placed 6 or 7 feet apart.
I'm not sure why, but few streaming speakers are available as stereo pairs. Why not? It should be a simple matter for Bluetooth or AirPlay speakers to recognize the presence of a second speaker, and send sound to the right and left channel speakers. I guess most buyers don't miss stereo, and mono is half the price of stereo, so why bother?
I can think of at least two really good reasons: the engineers and producers invested a lot of time perfecting your favorite music's stereo mix, and stereo opens up the spatial aspects of sound reproduction that mono totally misses. A stereo pair of tiny Audioengine2 speakers ($199) can liberate the sound in ways that more expensive single speaker systems can't match. Stereo may soon be relegated to only headphone listening; we'll see.