Thomas didn't recuse himself when ruling on court cases filed by the advocacy group his wife is a leader of. It's all voluntary, if a Supreme Court justice chooses not to recuse themselves there is no higher court to force them.

Note, a lot of these "x legislator owns y stock" stories actually turn out to mean "x legislator owns a whole market index fund".

Thomas aggressively refuses to recuse himself from cases that other justices consider an obvious conflict of interest.

But they have no authority to enforce their opinion, and Thomas absolutely doesn't care. He didn't become a judge to rule on things he has no opinion on. For him, conflicting interest makes it that much more important to keep his hands in.