It’s an excellent business model. The only real infrastructure you need is a website, and you can have a custom site made for $5-10 thousand. Then you just have the monthly bandwidth charges. The rest is just e-marketing, which can be done for free, or the cost of some e-mails lists. After that, the money just comes rolling in.
The best part is that other people do all the actual work. All you have to do is charge them for publishing on your open-access online journal.
What you are selling is essentially scientific/academic fraud.
Unfortunately, this is a good business model, even though it is a terrible scientific model, and so it has proliferated. We may be living in the heyday of dubious open-access scientific journals.
The open-access format itself is not a bad one, and there are some very successful and respected open-access journals, such as the PLOS journals. The idea is that, instead of charging a subscription in order to gain access to published articles (in print or online), the articles are open-access, but authors pay a fee to have their work published.