We could definitely do more - one of the challenges here is that some bacteria are quite picky about where they grow - ie there a lots that don't grow on a petri dish. So not always so easy to grow side by side.

Note from the paper - they stored the soil samples for a year on growth media before testing ( to allow any compunds to build up presumably ). That doesn't sound like a fast process.

Our knowledge of what's out there is quite biased by what grows well in the lab - probably less than 1% of all bacteria will grow on an agar plate.