The ACS recently hosted a virtual conference and there was an interesting talk on NMR experiments using the Earth's magnetic field. What surprised me was the number of molecules studied with Earth's field NMR so far is around 22. Another interesting aspect was that NMR at low magnetic field strength is richer in the number of lines as compared to the extremely strong magnets used today. I think spectroscopists might be happier if they get a rich spectrum (good for finger printing).
This site has many NMR researchers, my question is why Earth's field NMR never caught up? The number of molecules studied so far is very low. Is it theoretically very challenging or the analytical sensitivity is hopelessly low?