Rockefeller was convicted of being rich. That's the bottom line.
Here is a part of the majority court decision written by Chief Justice White:
"constituted a combination in violation of the first section and an attempt to create a monopoly or to monopolize"
>"entered into agreements with, various persons, firms, corporations, and limited partnerships engaged in purchasing, shipping, refining, and selling petroleum and its products among the various states, for the purpose of fixing the price of crude and refined oil and the products thereof, limiting the production thereof, and controlling the transportation therein, and thereby restraining trade and commerce among the several states, and monopolizing the said commerce"
If actual price-fixing to monopolize commerce isn't part of your unique definition of a monopoly, I don't know what else to tell you. It's pretty hard to price fix without a monopoly, but as we already discussed they were able to do so because they controlled over 90% of refineries at the time. (And before you jump in again - erroneously - about their price during the trial, this monopoly charge was related to actions decades earlier). But it's pretty obvious from your relentless rules-lawyering/wordsmithing that either you aren't responding in good faith or don't actually have the ability/willingness to read evidence objectively.
Cognitive dissonance is a hell of a drug.
I think a better question for you to ask yourself is “why did the court determine they were acting in a monopolistic manner?”
I’d suggest reading the previously referenced court ruling to get your answer.