If i'm trying to steel-man why, I presume because the read/write/edit tools use more context tokens because they don't support reading part of a file/etc.

So the agent is going to put less into context when it uses sed to see 15 lines of a file than using read and putting the entire file into context.

That is my best charitable guess at what they are hoping to achieve.

Of course, there is an obvious set of solutions for this problem that don't involve pushing the agent to use bash.