It’s making money on Shabbos.
You didn’t make money on Shabbos.
It’s certainly not a no-brainer, because stocks have also been discussed over the years as to Shabbos ramifications.
I don’t think anyone ever questioned owning stocks over Shabbos (or, at least, it’s pretty much been settled), even though the company is open over Shabbos and the value might go up (more relevant to Yom Tov since markets are open).
I think the issues discussed are orders to automatically buy or sell at a certain price.