I built the iOS Library (KeiserKit) for working with the M3i, so can provide a bit of insight into this. I'm not affiliated with Keiser or anything like that though I should preface.
These devices don't show up because they can't be connected to. At least for the M3i, don't know about the Concept 2. The M3i sends broadcast packets with its current data in (sometimes it's the data since last interval, sometimes it's current stats, depends on the bike's settings) as a non-connectable device uses less power which is exactly what you want when most of the power comes from batteries and possibly the peddling action itself (not entirely sure on this, wouldn't be a terrible idea though!). When you pull data from it, you have to be scanning for devices in-app and parse the broadcasted data from the device instead of getting a constant stream from connecting to it.
This does mean you have to keep the app open as iOS won't let apps scan when not in the foreground, but showing these devices in the bluetooth menu is unlikely to be something Apple will do any time soon as there's not much point in having non-connectible devices in that menu.
I'm doing a bit of research into what people would want to see in an app that's friendly with the M3i though, so if you'd like to give some input hit me up: me@benwoodford.co.uk
