Most search engines can perfectly handle special characters. Some don't. If you remove them, then your site would be easily indexed by those search engines.
Additionally, special characters are usually turned into the awful but handy %xx patterns which can turn a readable URL into what seems to be a character soup.
So I think it is a little of both reasons: technical and aesthetic.
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July 15, 2020: Q2A 1.8.5 released!