They watch Hikaru because he is fun while he plays and wins.
Offline, he is #4 is slow chess and #1 in Blitz.
He's not facing strong challenges on Titled Tuesday, and (like all top players) he is so good that there simply aren't enough players and data to make the empirical Elo scale work for assessing his win probabilities.
But they have tutorials, put tons of effort into entertaining content, etc.
Hikaru doesn't.
People watch Hiraku because they want to watch a top 5 player.