This article[1] from Brookings says,
>> At the time of the divestiture, the oil industry was becoming competitive because it was moving into Kansas, Oklahoma, Texas, Louisiana and California—states where Standard Oil didn’t have much power. The price of petroleum was actually falling in the years before the case, because these new fields were pumping so much crude. The breakup had no measurable effect on oil production, crude-oil prices or refined-product prices.
(The article does say that antitrust actions were necessary to make cigarettes affordable, though.)
For a rather less charitable take, [2] from the "Competitive Enterprise Institute" says,
>> Standard Oil Co. of New Jersey v. United States had a defendant that was cutting prices while increasing output. The case also lacked evidence of either predatory pricing or consumer harm.
After this quick bullet-point summary, there's more content below with references to other academic sources, page 2 is pretty interesting.
> many would consider social media companies to be natural monopolies in the current context
They have positive returns to scale, but even this phrasing ("social media companies") deflates the argument -- Facebook competes with Twitter competes with TikTok competes with Reddit competes with Youtube etc. They're big enough to exert market power, but
- Some of them seem to dislike using that power (to the horror of authoritarians in many governments who want to co-opt it), and
- If they abuse that power to the detriment of users (raising prices too high, banning enough communities) users will go elsewhere.
1: https://www.brookings.edu/opinions/if-it-aint-broke-dont-bre...
2: https://assets.realclear.com/files/2021/01/1755_antitrust.pd...