Publishing companies exist because faculty need to publish in "legitimate" journals; this is an even bigger issue in Europe than in America. Basically, if a young professor is trying to gain tenure, the university will insist that she have a solid record of published researched. The only publications they will consider for a tenure decision are those that are in journals published by the big companies, because those are what are considered "legitimate."

Technically journal publishing companies have been obsolete since the Internet was invented, but the problem is not technical, it is political. Even in the crypto research community, which maintains its own repository of research papers (https://eprint.iacr.org/), there is still a need to have Springer publish conference proceedings.