Company A raises prices and reports record quarterly profits. Company B is aware of this because both the price raising and quarterly profit report for Company A are public. Company B raises prices too so that they can get also get more profit. Company C either does the same thing, or there is no company C because rubber stamped mergers and acquisitions for decades have allowed a handful of companies to dominate every industry, sometimes multiple industries.

None of this is a conspiracy. It's Econ 101 level "how things work."