It matters because the Democrats win on turnout in this country. When people are enthusiastic about a candidate, they stand in those four-hour poll lines designed to discourage them from voting. When they aren't, they don't.
I live in GOP territory in a red state. My precinct might contain 300 people. I walk five minutes to the polling site, cast my votes immediately, and walk home. If it rains, I drive. My votes never count, in the sense that I haven't voted for a winning candidate (meaning the Electoral College for president specifically) in a general in over a decade, but no one's stopping me. On demographics, the odds are I vote Republican, so they let me do it without fuss.
That is the experience of many Republican voters, but it is not that of a sizable minority of the Democratic base.