Let's not forget that these sales by management are planned MONTHS in advance.
They don't AND can't wake up one sunny morning and decide that, "Hey, it's a great day to sell. I think I'll dump some stock and buy that Patek Phillipe!"
To prevent the slightest suspicion of corruption, impropriety, true "insider" trading, etc., CEO's and management MUST set up a prearranged plan with the SEC, a 10b5-1 plan.
They MUST make arrangements, months in advance, to sell chunks of stock. That’s like you or me having to decide months in advance when, exactly, we will go to the bank [or credit union] to withdraw a predetermined amount of cash.