It has become a thing in the las 5 years or so. First bifacial modules had to get more popular and overall cost had to go down before it made economic sense to farmers.

They can't be more widespread. They need to be thin and exactly vertical to optimally work.

Sorry, I couldn't resist

Because it can be a pretty steep hit to power output/efficiency compared to angling them to face the sun.

Cost per watt is significantly higher this way compared to what you generally see. It allows more sharing of sun between other uses and solar, but it comes at the expense of not letting the solar get as much sun for the same panel cost.