They work so well because the barrier is extremely low: it's literally a single interaction, keep the "button" pressed and the message is sent automatically upon releasing it.

And yet nobody was using voice messages when you had to: - Tap "attach" - Tap "audio" - Tap "record" - Tap "confirm" Or, worse, use a separate app and "share" to WhatsApp.

UX is important. I assume this service is based on a similar principle.