heh. It's not so much because of the microphones that the data sets are THAT narrow band - it's more phone bandwidth limitations. Even the cheapest electret and MEMS mics have pretty good freq response, far beyond 4khz (nyquist 8khz) this data set uses.

Now that bandwidth is becoming less of an issue, we will be getting less shitty sounding, wider bandwidth phone audio - https://en.wikipedia.org/wiki/Wideband_audio

Though if I had it my way, U87 or U47, or hey even SM7B would be mandatory for all speech recordings :)