Because the system is rigged in more ways.

I will try and keep it short.

There is a metric associated with scientific journals called impact factor. You can read up somewhere how its calculated but it is essentially a number that boils down how often a journal's papers are cited.

The higher impact factor your paper gets from getting published the better you look. Its reputable.

This stuff is important when you apply for research grants or new positions within academia. If you have a candidate that published regular high impact versus one that doesn't, there isn't much reason to choose the one that doesn't.

However, as you might have guessed, the system is flawed and one shouldn't rely on impact factors as a measure. However, everyone keeps doing it because it is a simple 1 number metric and everything else is a lot more work to evaluate quality with.

Now a new journal cannot just come in and offer cheap prices because they start without or with low impact factor. They have to build that first over several years with fantastic papers cited by tons of people. You cannot achieve that easily.

Sounds great right? Scientific papers essentially reinvented printing money and now act as if there is no other way to handle this. Add to that, that they give no two craps about scientific integrity or misconduct and there is a small hope scientists might slowly get fed up with the system.