They're not hard to pronounce, they're just long and unfamiliar, because many of them are conjugate words whose components are borrowed from Greek or Latin.
The medical profession needs to be very specific when discussing diseases. Otherwise you might run into the problem of coming down with "the French disease" while in France, where all the doctors will want to treat you for "the Italian disease", or ship you off to Russia and treat you for "the Polish disease".
Or, y'know, they could just treat you for syphilis.