I’m late to the discussion and on mobile but I think Milieu 0 has a good suggestion of why there is not much ‘tech sharing’ within the 3I. One of Cleon’s opponents Baron Yandl Willer who we are told died in a car accident before giving a speech to the Moot says the following:
And as we form this great brotherhood of new worlds, are we really making life better for these people? NO! Have any of you actually read the IISS contact manuals? The teachings of ‘The School’? Every core principle of the exploration and re-contact is based on making them into consumer nations so that Zhunastu Industries can rape their resourced and then sell them back the goods manufactured from their planet’s life blood...
A darker more cynical look at the Imperium provides the suggestion that the more important worlds keep the tech levels of lesser worlds low to provide a balance of trade that favours them. The 3I is a mercantilist empire at its heart and more powerful nobles and corporations are associated with higher tech worlds that have a vested interest in obtaining raw materials cheaply and selling finished goods to the worlds they obtained said materials from.