The World of Fonts. Actually, it is amazing that the simple idea of dropping serifs at the ends of strokes didn't occur to the great many typographers who experimented with their shapes and sizes so much. In part, it is due to the inertia of scribes' tradition who, with their quills, simply could not produce a reasonably clean cut of a stroke.
Serifs help the eye to stick to the line and thus facilitate reading.
But the biggest part of the serif persistence was, of course, due to plain habit. The resulting blend of geometric consistency and aesthetic awkwardness may be disputable, but it was at least something quite new, and therefore impressive, at that time. This didn't happen, of course. Moreover, Futura itself didn't manage to become so neutral and familiar in the mass perception as to become a standard sans serif font for all occasions. However, it cannot be denied that Futura played an important role in sans serif becoming a mainstream type style, an accepted contrasting pair for the time-proven serif fonts.