With lots of PR around the launch of Meercat and Periscope (mobile apps which allow easy live streaming from a mobile phone) it may be worth quickly reviewing the potential demand and success of these new apps.
Live streaming from a mobile device is not new and Ustream have been providing that capability for some time - albeit that the app often crashes on my phone. However the speed of mobile networks has significantly improved making the whole process more viable.
In addition the timing may be right now. Microsoft will remember that they introduced the touch screen tablet before the IPAD but for a variety of reasons it did not grab the consumer - until Apple waved the magic wand. The second mouse often gets the cheese as they say / even a blind squirrel eventually finds a nut etc etc.
The profile of these new apps is such that Bob Bowman President and CEO of MLB advanced media has stated that the MLB are relaxed about fans using them. IP lawyers generally get all excited about these apps as technically the copyright is owned by the camera / phone operator - although conditions of access on tickets generally prohibits filming.
YouTube has had live capability for some time but so far the profile of the VOD aspect of the channel is much greater.
The answer to the question may be that live video is simply a much more difficult medium to make work and be visually appealing especially from a single camera or now phone. Live events that are "no-brainers" for live video coverage such as major sporting, news, music and cultural events are generally well covered at high cost.
With web cam / laptop costs where they are any event which is not totally spur of the moment will probably warrant more than "single phone coverage" possibly interrupted by an incoming text or call.
So it seems probable that if when walking down the street you suddenly spotted Elvis Presley (he lives) you would certainly try and grab a picture or video and publish quickly via social media but would the desire be there to "go live" ?