Wearables doesn't need much data
The primary comms technologies for wearables are ANT and Bluetooth Smart/LE.
Both these are designed around the idea of very low amounts of data sent in short bursts. This is done to save power. These devices spend almost all of the time sleeping. They wake up, send data and go back to sleep all within a few milliseconds.
That does not generate exabytes of data and never can. The constraint is in the batteries and the comms these devices use.
Of course all this data implies someone is later downloading reports and pretty graphs etc. But as we really can only do one or two things at a time, that does not increase data. All the time we spend looking at our heart rate charts is time we are not watching kitty videos.