In a dialogue, each speaker's turn needs its own reporting verb, and the verb must name what that turn was doing.

A dialogue is a sequence of different acts — asking, answering, objecting, conceding. Reporting all of them with 'said' turns a conversation into a list and loses precisely what the passage was about.

He asked whether she was free; she replied that she was not.

one verb of asking, one of answering

He said that she was free and she said that she was not.

'said' twice, so the exchange is lost

Where it bites

Comprehension questions on who conceded what. The reporting verb is the evidence, so a passage that reports everything with 'said' is one where the answer must come from the content instead.