Fidaxo also may not be that great or cost effective[1]. Optimer, I believe has been bought by Cubist and delisted from Nasdaq. 1. Clin Infect Dis. 2013 Aug;57(4):555-61
I do know their most promising findings don't get reflected in clinical trials well. But "The Drug Companies aren't there" isn't addressed by a small drug company specializing in ID getting bought about by another drug company that has tons of ID products for half a billion dollars.
I also really don't buy the "return on investment" argument, as curing a bacterial disease rarely provides immunity.
It's also not my experience as a researcher in the area - several drug companies are actively funding research.