Then they are useless. Send us the boss directly, will save a layer of communication.
Problem is the boss wants a unique interlocutor, and one who says yes. Then if he is friendly enough, engineers will prefer to do a shitty job (rush "features" and even more bugs) rather than inconvenience their manager who already committed on behalf of the whole team.
Or they just want to cut out unnecessary layers. You don't really want an extra level between the group demanding the features and the group implementing them.
Feedback about technical feasibility, time to implement et cetera really needs to go directly to the group demanding the feature, and their responses need to come directly back to the group implementing it. A competent middle man can help those two groups interact, but generally adding an extra middle layer reduces everybody's ability to function well.
Problem is the boss wants a unique interlocutor, and one who says yes. Then if he is friendly enough, engineers will prefer to do a shitty job (rush "features" and even more bugs) rather than inconvenience their manager who already committed on behalf of the whole team.