The strongest answer is that bluetooth beacons don't work well in huge infrastructure. Sometimes you don't have a place for them to go or they get stolen. Also it's free to use the speaker infrastructure, but outfitting and managing hundreds of beacons is not cheap. Some of our clients have switched to audio beacons for similar reasons.

The Brooklyn Museum did a nice writeup of why bluetooth beacons at scale didn't work for them.

https://www.brooklynmuseum.org/community/blogosphere/2015/02...