I think there's a few reasons. I agree with Bobsy about watching Chelsea Vs Liverpool yet again. We get so many opportunities to watch such fixtures in the league and Europe that it hardly has the same excitement, particularly in a tournament many sides use as experience for the reserves.

The earlier rounds are generally more exciting than the later ones.

Play the semis away from Wembley, making the final venue special and more prestigious.

3pm kick off.

No other football on the same day.

Hours of build up on TV.

Exhume Saint and Greavsie.

Etc