Use increased slowly, for several reasons. Biologists didn't want their work to be 'scooped' and some were afraid that papers in bioaRxiv wouldn't be accepted by journals for peer review and publication.
Last month the Howard Hughes Medical Institute hosted the ASAPbio meeting to give all the players in the biological scholarly communications space a chance to discuss how to include pre-prints in their current ways of work. The program and video are available to anyone interested.
Get involved! Discuss the benefits of submitting to bioaRxiv with your lab mates, profs, even your librarian. Join the conversation on Twitter at #ASAPbio. Post a selfie of yourself submitting your paper.