A: You're correct that after the Nominations Committee has reported and after nominations from the floor are closed, nominations are over. Why should the members be allowed to vote for someone who wasn't nominated? Let's look at a hypothetical situation that may explain the reasoning.

Suppose two persons have been nominated for office. Each has the same amount of support, and when the votes are counted, it's a tie. No election. Now assume none of the supporters is willing to vote for the other candidate, whom they hate, distrust, ... whatever. The name of a member who, although not ideal to any voter, is acceptible to a majority of them. If write-ins were not allowed, they could not vote for this alternate.

Real-life, non-nominated write-ins have won elections in similar circumstances. In general, the flexibility is valuable.