We are forced to.
For example, in my country, every assessment we have to take (be it for a tenure-track hiring process, for getting tenure, for asking for a grant, etc.) has as the most important criterion "publications in journals indexed by ISI JCR" together with their quartile.
Most of the journals in ISI JCR follow this model where they cost money (be it to publish or to read) and provide very little value... except for being on that list and being necessary to (aspire to) stay in academia and feed your family, of course.
Other countries have better systems in the sense that they may be more open to other venues not in ISI JCR, some may even actually look at the quality of the papers instead of just blindly following rules to score quartiles. But scientists everywhere have the same problem in larger or smaller degree.
A solution that is sometimes proposed is that authors who are no longer struggling for their career (e.g. tenured full professors) take a stand and refuse to publish there. Some movements have been made in that direction, e.g. in mathematics. But in most fields a senior professor will work together with Ph.D. students and postdocs who are in the struggle, so it isn't realistic either.
The truth IMO is that the solution must come top-down, from governments. The EU has made some progress, e.g. mandating open access for EU grant holders, but what happens then is that publishers will let you make your paper open access in exchange for a hefty fee (which again, is paid from taxpayer money). The real solution would be to mandate by law that research paid by taxpayer money is published in non-for-profit venues, period.