For most large animals they don’t have the dexterity to keep the majority of flies off, or their hide is thick enough that the large animals don’t notice, so flies can easily feed on their blood and sweat. Animals will have tails to keep flies away from the anus and prevent flystrike for the most part, and eyelids/lashes to keep them away from eyeballs/eyeducts, so the most important exposed parts are by and large protected. The rest is just nuisance/not noticed.
For most large animals they don’t have the dexterity to keep the majority of flies off, or their hide is thick enough that the large animals don’t notice, so flies can easily feed on their blood and sweat. Animals will have tails to keep flies away from the anus and prevent flystrike for the most part, and eyelids/lashes to keep them away from eyeballs/eyeducts, so the most important exposed parts are by and large protected. The rest is just nuisance/not noticed.