Because the hackers who are out there are not really after the businesses. They are after your computer. . . and the updates always contain more security updates and improvements that keep your computer safe from those hackers than stupid mistakes like this especially idiotic one which really did not put you at all at risk from any of them because it required anyone who wanted to exploit it have physical access to your iMac.
When I 1st read the alert I thought it required some one sitting at the device. I typed “root” in one time to see the result and it didnt work so i waited a day and saw your post. Swarched for the update and saw it. You were ahead of the curve on this one fer sure and thanks.