I’d think if the stock holdings are too great and in place for too long it might violate the charter and mission.

Not really because both of those are set by the company in question unless there are specific government regulations for that industry.

I’m talking about public companies. People didn’t invest in a company just to have them go invest somewhere else.

Sometimes they do. An example in Australia is Woolworths, our largest supermarket, they also own Kmart (a clothing store) BigW (a general store), BWS (an alcohol store), plus have a lot of land holdings for those stores.