Tax payer money is already funded to conduct research. Why do we need to pay 2000$ to host a PDF article?

You do not need to pay to host a PDF article, there are platforms such as arxiv.org or zenodo.org that do this for free for you.

Yes, but as others have said, professional advancement typically depends on publishing in the expensive journals. And that's no accident, in that predatory for-profit publishers have targeted prestigious journals for acquisition. It's the same game that drug makers play with top-selling drugs.

Eventually, authors will migrate to the not-for-profit open access journals and platforms. But that will take time. Top-ranked PIs must lead the way, given that their reputations are well established, and they have tenure.

Supporting research is an excellent use of tax payer money. But paying monopoly rents to publish? Not so much, I think.