Tableau worksheets and dashboards are proprietary and need either Tableau Reader on the client’s desktop or Tableau Server to run proprietary server side stuff for the js libraries to draw it. This is expensive to license their server and limited in how you can host. In many situations the data is small enough to send to the client.

It would be nice if tableau would just generate static content that could be hosted anywhere.

There’s not a client tool for d3 as nice as tableau. I work with lots of scientists who learned tableau but aren’t really programmers and can’t figure out d3 or other libraries.

Maybe they meant salesforce's business model, which doesn't usually include outputting stuff in an open format? I'm not sure.

Sort of. Salesforce is more interested in selling cloud licenses and space. They push proprietary apps and such, but maybe they won’t care so much about hosting tableau server specifically.