It's that when someone that you only knew from online is reported to have died, you can't help but asking yourself if it's true. So you wonder if you should feel sorry or if it's misplaced sympathy.
And you have no way to know.
Because of everyone who reacts to it, you don't even know who possibly knew the departed one IRL. And of those who say they do... You still wonder if they aren't the not-dead-one under another name.
Reason #2462 why you shouldn't get too involved emotionally online.