Seems to me like they did show up. A 3 million popular vote spread is pretty significant. Of course, the popular vote isn't what wins an election, but those people certainly showed up.
The popular vote is irrelevant to US politics. Hillary clearly lost because the voting base that normally shows up for Dems did not show up for her. Trump did no better than previous Republican candidates.
This graph is deliberately misleading, especially for the point you're trying to make. Starting the Y axis at 52k creates a visual exaggeration of the difference between turnouts, and omitting elections prior to Obama obfuscates the fact that Obama's election turnout was a historic and unprecedented outlier. If you include previous elections, it will show that Hillary Clinton received more votes than any other candidate in history besides Obama.
Obama's record breaking turnout does not represent "the voting base that normally shows up for Dems".
http://www.politicususa.com/2016/11/09/graph-shows-hillary-c...