https://en.wikipedia.org/wiki/Omission_bias probably? "Omission bias is the moral judgement in which people prefer omission (inaction) over commission (action), and tend to believe harm as a result of commission more negatively than harm as a result of omission."

It just isn't provable, I think it it is technically illegal.

Holding stock knowing it might go up is illegal? I don't think that's technically illegal.

If you were going to sell but learned something non public, then letter of the law says you can't make a decision to no longer sell.

that's explicitly false - https://en.wikipedia.org/wiki/SEC_Rule_10b5-1#A_possible_loo...

*because of insider knowledge

I think the law says evidence needs a purchase or sale. Relatedly, the failure to purchase is not evidence.