They are not engineering serendipitous conversations
Professionals react to “help requests” or ask for “tips, information or help” in an ad hoc manner across networks. Often, they don’t ask or give, just out of inertia. For the asker, this creates friction, and they don’t ask in the network the next time around. The networks don’t do a good job of parsing the person’s connections to suggest which subset should they target their broadcast to for a given context.
The nudge to ask and the nudge to give has to be explicitly designed till the habit forms.