Data.gov and Science.gov provide access to information that can also be found via USA.gov, but they're better when you know you're looking for data or STEM research.
In 2013, the Office of Science and Technology Policy issued a memorandum, “Increasing Access to the Results of Federally Funded Scientific Research” (PDF), stating that all government agencies with research budgets of $100 million or more must develop a plan to make the results of that research (article + data) available to the public. This was followed by another memorandum, "Open Data Policy-Managing Information as an Asset" (PDF) which ordered that agencies "must manage information as an asset throughout its life cycle to promote openness and interoperability." As a result, over the last several years, research and information produced or funded by federal agencies has become more and more available to the public.
Note: Unlike articles and other works published open access, which means free to read and reuse, public access works, while still free to read, are not necessarily free to reuse and may include an embargo period between being published and becoming publicly available.
Since the 2013 memo, the residents of the White House have generally supported increasing public access to non-sensitive information and data produced by the federal government. In 2019, President Trump signed an omnibus bill that included the Open, Public, Electronic, and Necessary (OPEN) Government Data Act, which made permanent some aspects of the 2013 data memo and established that government information should be produced as machine-readable data rather than documents. Federal agencies are now required, if they hadn't done so already, to develop an open data plan that ensures that data is in "an open format and under an open license," and those agencies will also have a Chief Data Officer to oversee the efforts.