NTT researchers recently demonstrated ability to transmit 100 Gbps at 300 GHz frequencies, far beyond the ranges we have used for freespace communications in the past.
One reason mobile and fixed wireless bandwidth is climbing is that we now are starting to use higher frequencies. That matters because signals at higher frequencies inherently can carry more data. And more than physical bandwidth is involved. Any given unit of capacity at a millimeter frequency will have the ability to carry more data than the same unit of capacity at a lower frequency.
As a simple example, assume that every zero crossing of any wave represents the opportunity to code a bit (one or zero). Using a very simple coding, the total amount of bits that can be represented in one second of time hinges on the number of oscillations a wave makes over that period of time.
Higher-frequency signals make more crossings, and therefore can represent more symbols. And that is why millimeter wave signals have such high bandwidth: there are simply so many more zero crossings in any unit of time, compared to lower-frequency signals (600 MHz to 800 MHz or 2-GHz, for example).