...then how do you maintain an adversarial proceeding?
Like, it's a pretty basic part of American law that courts only hear "cases and controversies" - that is to say, you need to have two parties who disagree before judges are allowed to do anything. If both parties no longer disagree, a settlement is how they call the lawsuit off. But if they're not allowed to settle... what happens? Are we going to force both parties into the court to argue positions they no longer hold? Like, what stops the government from just arguing the case really badly to intentionally lose? That would be worse: now, instead of a prosecution leading to a weak settlement, you have every weak case being carried to term, resulting in a miscarriage of justice as each judgment forms negative precedent against future antitrust action. This is a recipe for eroding antitrust faster.
What you're thinking is that government lawyers are just there to extract the settlement, ergo if we force them to go for the kill, they will get more kills. The reality is that the current social class of lawyers and judges hate antitrust. They successfully recast it from an argument about market power to an argument about price controls, and well, most monopolies don't actually raise prices[0], so building a case against them is very difficult.
Hell, in the Microsoft lawsuit, the reason why the government settled was because the initial judgement to break up Microsoft got thrown out, because the judge who issued it blabbed about it to the press. Keeping the case going would not have produced a better outcome than a negotiated settlement.
Furthermore, while the current "monopoly is about prices" argument is new, the judicial contempt for antitrust is not new. It took three tries and FDR threatening to pack the courts before we got judges consistently applying antitrust law as anything more than a mere ban on unions. While courts are ostensibly neutral arbiters of law, they bend to the fiscal interests of the nation and are inherently political entities, because courts have no inherent power but what they are given by the state.
Or, in other words, if you want more antitrust breakups you need Congress to start appointing more neo-Brandeis leaning judges.
[0] Strictly speaking, there are lots of businesses where monopolies are economically efficient. A monopolist that raises prices is