There was a change in the enforcement of antitrust law in the 1970s. Consumer welfare, which came to mean lower prices, is the standard. Effectively normal competition is fine and takes egregious behavior to be violation. It even assumes that big companies are more efficient which makes up for lack of competition.

The other change is reluctance to break up companies. AT&T break up was big deal. Microsoft survived being broken up in its antitrust trial. Tech companies can only be broken up vertically, but maybe the forced competition would be enough.