Beginning with a discussion of how collections diversity has been conceptualized and assessed within the literature, we then analyze four areas in which professional practices and modes of thinking create barriers to collecting materials from historically marginalized voices. Specifically, we discuss how metadata practices can obscure these materials from acquisitions workflows and user discovery, how relying on use statistics can reinforce existing inequalities. Finally, we discuss how understaffing in key areas and budgetary constraints impede libraries from recognizing and addressing the full scope of the problem.