why did the early films use so much eye makeup, even on the men?

I do not know the answer, but could I venture a guess?

There is a saying that "the eyes are the windows of the soul." An actor's eyes and what he does with them are very important in creating and playing his character. An actor on stage must make up his or her eyes. The audience is watching -- usually -- from 30 or more feet away. The harsh stage lighting also washes out one's facial features. Heavy eye make up helps the audience to see an actor's eyes and what he does with them.

I cannot help but wonder if the heavy eye make up in the 1910s and 1920s is a carry-over from the stage. Eye make up like this disappears in the 1930s.

Just a thought . . .

There was at least one Laurel & Hardy silent in which the two leads wore exaggerated makeup to emphasise their facial features. They perhaps decided that it was a ploy which did not fit in with their style of performing - they quickly dropped the experiment & returned to 'natural' faces on screen.