3 ideas
The real obstacle to contact with extraterrestrial intelligence is the gap between minds shaped by different histories, not the physical distance between stars. Crossing space can be solved with engineering, as the black-hole maneuver shows. Crossing that gap cannot, because each side reads the other's signals through categories the other does not share.
When one side cannot read the other's intentions, it treats silence as hostility or evasion and answers with a show of force meant to compel a response. The target reads that force as proof of aggression and responds defensively. Each move confirms both sides' worst assumptions, so a demand for contact turns into war.
A civilisation locked in a military rivalry may extend its competition into orbit, converting its planetary surroundings into weapons, shields and camouflage. A civilisation at that stage treats every outside signal as a possible enemy move, so it cannot afford open contact. This offers one explanation for the silence of the universe: listeners who find such a civilisation meet a fortress rather than a partner.