If you look back historically, the idea that monopolies were broken up because of their ability to raise prices without the check of competition just isn't really telling the full story. Consider this from the Congressional Record of the House (1890) by a proponent of the then under debate anti-trust act (https://www.congress.gov/bound-congressional-record/1890/05/..., page 4100):
"Some say that the trusts have made products cheaper, have reduced prices; but if the price of oil, for instance, were reduced to 1 cent a barrel it would not right the wrong done to the people of this country by the "trusts" which have destroyed legitimate competition and driven honest men from legitimate business enterprises."
The argument wasn't that the "trusts make products -cheaper-" idea was wrong, but that it didn't matter.
The only way to maintain a natural monopoly is the ensure that the barriers to entry for competition are sufficient to make new entrants unviable. One way to do that is to leverage economies of scale to lower prices to the point where a new entrant simply can't compete on price.