Because there's an obvious implication that Trump is pushing the drug because he has a financial interest in pushing the drug. But if his financial interest is so small that he stood to gain hundreds of dollars, maybe thousands at most, then implying he's doing it for financial reasons is extremely dishonest.

There's a big space between "implying he's doing it for financial reasons" and "reporting on the presence of a financial interest". It would be worse reporting to _omit_ the financial interest rather than include it.

I probably have a proportional exposure to SNY via index funds as what Trump is reported to have, compared to his fortune. I would say that there would be very little value in reporting that interest in any context. Certainly it would tend to make most readers think that the financial interest may serve as an improper motivation, when there is no likelihood that that is the case.