FWIW, I don't look at each and every filing, but the footnotes often indicate the sells are due to pre-established trading plans under rule 10b5-1 ... which allows major holders "to sell a predetermined number of shares at a predetermined time. 10b5-1 plans are used by many corporate executives in an attempt to avoid accusations of insider trading."
INVESTOPEDIA EXPLAINS 'RULE 10B5-1'
It is not uncommon to see a major holder sell some of his/her shares at regular intervals. For example, a director of XYZ Corporation may choose to sell 5,000 shares of stock on the second Wednesday of every month. To avoid conflict, 10b5-1 plans must be established when the individual is unaware of any material non-public information.