They replaced the old website with a new website. The old website is stored in: https://obamawhitehouse.archives.gov/ This is usual. Obama toke the same measure. Here is the Bush website if you like it: https://georgewbush-whitehouse.archives.gov/
With the change, Trump (technical staff) removed many subject they disagree, and many subjects they agree with. If Obama had a page about how great are ginger hair people, it would have disappeared too.