Quite obviously they're ridiculously fun. How magical must those colourful, floating orbs be to babies?! As a speech therapist, I've recommended parents play with bubbles many times and for many reasons, e.g. Turn taking, communication temptation, practising 2 syllable words (bu-bbles), practising the /p/ sound (pop!), supporting intentional communication, or simply as a way to have fun together!
We've introduced bubbles as a fun, new sensory play - August is just moving past the 'wowwww' phase and is working on his hand-eye coordination to pop the bubbles! I'm using it as an opportunity to model the signs for 'more' and 'again' as well as the words
⋒ blow the bubbles.
⋒ when they've all popped, WAIT and look at your baby expectantly.
⋒ when they make eye contact, smile and say/sign 'more' or 'again', before blowing the bubbles again.
⋒ when baby is a little older, you can wait until they try to sign or make a vocalisation (a noise) before blowing the bubbles - which teaches them that their communication makes the bubbles happen!