It isn’t, but to get a full professorship, you need to publish in higher ranked journals. APC-Open-Access is just another iteration of the parasitic business model of the few big publishers. In the end, universities pay the same amounts to the publishers as before, or even more. This business model can only be overcome if and when academia changes the rules for assessment of application to higher ranked academic positions. There are journals that are entirely run by scientists and scientific libraries. Only in this model the peer review and publishing platform becomes a commodity.