There has been a massive wave of bot and probably real human activity to supress assasination talk on line. Wouldn't be surprised its because of this. Even in these comments from these farms trying to downplay Kamala and Biden, posting obviously false information.
I think it's pretty obvious that the assassination attempt will not generate good discussion.
Most online platforms are just a collection of spicy take memes about the event.
In case of Biden stepping down, there's a lot more to discuss, ranging from his legacy as a statesman to the future of the election.
If there was a leftist bias don't you think it'd make sense to promote a story of Trump getting shot by his own base? Sounds like there's a right wing bias.