Why does bluetooth (still) only support pairing two devices?

Question

When bluetooth was first devised there was typically only one device to connect to at a time so it was quite natural to just implement a pairing protocol. I believe we are now on Bluetooth 5

Why is it that:

• Each device may typically only pair with a single other device?
• Even in devices that have multiple bluetooth capable chips only one is used.
• In contrast with the profileration of usb hubs there are very few bluetooth hubs on sale and they are relaitvely expensive (e.g. the CASSIA which seems to have been discontinued)

I note that there is now "dual audio". Allowing you to pair with up to 3 (which is more than dual!) audio devices but this is not what I'm after.

Referring to this article one bluetooth master can support up to 7 slaves.

However if we consider some basic IoT scenarios this does not match the requirements very well. Consider:

• I have one or more bluetooth speakers in my home

  • I would like to be able to send music to one from any device:
    • My phone
    • My partners phone
    • A PC
  • Without having the speaker or the audio source forget the previous connection.
  • Only one can stream at a time so maybe the devices have a priority or one lends the connection to another.

• I have a phone and I want to connect:

  • a smartwatch
  • bluetooth headphones
  • a heart monitor
  • one or more speakers as above

• I might want to lend a device to someone in my household (e.g. the headphones or heart monitor)

To my mind this suggests we want a peer to peer network like we have with WIFI or ethernet. So why hasn't bluetooth evolved in this direction? It seems it have if I google "bluetooth piconet"

It looks like the second scenario ought to be supported (the phone as master and the rest as slaves) but I commonly find in android at least that pairing one device causes others to be disconnected. Is this because the slave needs to be a master temporarily to configure it?

How much of this is a 'mere' software issue and how much is down to issues with the protocol and technology itself?

I think the answer is that its down to the software. Any device wanting to act as the 'master' needs to support creating a piconet which is more advanced than you find in the average smartphone software. But this begs the question (as old as the invention of software) why isn't there better software?

I think I've mostly answered my own question here but perhaps someone out there can offer further enlightenment.

Related:

• Make two bluetooth modules communicate directly?
• Bluetooth Concurrent connection
• Pairing to a module containing multiple Bluetooth units
• https://electronics.stackexchange.com/a/430258/270158
• https://stackoverflow.com/questions/5005253/establishing-a-bluetooth-piconet-in-android

See also

• https://en.wikipedia.org/wiki/piconet
• https://en.wikipedia.org/wiki/Scatternet

Answer 1

Bluetooth 5 allows up to 8 connections at a time.

Android P allowed up to 5 audio devices connected at a time (developer mode), but active streaming was still only allowed to less at a time.

The standard allows for more than what developers want to support. Google or Samsung or whomever doesn't think anyone wants or needs to stream music to 5 audio devices at a time, and the more you can stream to the more complicated the coding and debugging would get, for diminishing returns. Basic cost vs benefit analysis. Both iOS and android drop features every release because the majority of people don't really use them.