Because Napoleon was the first ordinary person to rise up to the level he achieved in Western culture.

We are used to such achievement now, we even undermine such extreme rises (their parents helped them out, they were middle class not poor, etc) but people forget before Napoleon that rise from non-noble to Emperor had never happened since classical times.

Of course both people who could never dream of such achievements and also the useless rich, insecure in their position, both dislike him.