It would appear that Richard Castellano had the day off when that scene was filmed.

Either that or he simply couldn't fit throught the door.

No other reason in terms of the characters and their relationship with Don Vito.

Apple

A wise and frugal government, which shall leave men free to regulate their own pursuits of industry and improvement, and shall not take from the mouth of labor the bread it has earned - this is the sum of good government.

- THOMAS JEFFERSON