Part of the challenge is the reputation issue. Academics want to publish where there is prestige, which means there has to be a perception of the venue as good. This typically either comes from reasonable gatekeeping and high-quality peers (e.g. arXiv) or pushing metrics (e.g. Nature Publishing Group journals). Generating an attractive journal is non-trivial and few people with the appropriate knowledge and expertise take the plunge would do so without some guarantee of profit.