Solicitors working on many cases at the same time, they respond to emails and letters as fast as they can but you are in a queue. So they review something, send you an email or letter with a query, it may take you several days to answer, then you wait until they get around to your answer which may raise another query, rinse and repeat.
Then some people are just bananas. My BIL told us he could not give the executor his pps number (because he was a beneficiary) as he was still grieving the death of his parent and it was too soon to ask. The same guy a few months later was querying the delays as he wanted his money.