Why do I have to wait as a proposer until all questions are in before I can answer them?

Proposers are required to wait until all questions are in before answering them for two reasons:

It helps minimize comment chaos. Proposers will often try to get ahead of questions by anticipating what other participants may ask. Instead, Murmur gives participants the chance to comment and ask questions in an unbiased and uninfluenced environment.
It gives the proposer a truer signal of the level of understanding across the team. Allowing everyone to ask questions before the proposer can answer gives a more accurate picture of how widespread any confusion may be. If a proposer jumps in to answer a question from a single participant before anyone else has had the chance to contribute, the proposer isn’t benefiting from a full dataset and may be making inaccurate assumptions.