Sad Spider-Man Villain Backstories we are never going to get.

Carolyn Traynor watching her beloved mentor/father figure Octavius succumb to his wounds from Oscorp Sabotage.

Max(imillian/ine) Dillon learning how to put others before him/herself just in time to drown in Osborn's Koi pond after taking a bullet for one of the other Sinister Six

Kraven the Hunter blowing his brains out after beating Spider-Man because it was the only thing he still had to live for after his wife took the kids.

Curt Connors (who lost his legs to an IED in the MCU) receiving a weaponized cure (like the anti-cancer bullet) watching his legs melt before his very eyes, before being executed by Osborn so that no one could trace the Lizard back to Oscorp. Martha and Billy spend the rest of their lives believing Curt abandoned them.

Aleksei Sytsevich's parents getting killed by Ultron's Drones in Age of Ultron and having to provide for his siblings by moving to America and becoming hired muscle, agreeing to be injected with Emil Blonsky's blood sample and becoming permanently trapped as "The Rhino."

William Baker disintegrating after being bitten by Carnage, his last thoughts being of his poor elderly mother's mounting hospital bills.

Disgraced Police Officer Mac Gargan losing his badge after accidentally killing an eight-year-boy during a shootout with an armed suspect, forcing him to accept seedy PI jobs.

Eddie Brock, disgraced, disowned, divorced, and diagnosed in church begging for strength he no longer has, and having his prayers answered by "powers from above."

(Adrian/Adrienne) Toomes putting on his/her older brother Riley's Wing Suit for the first time.

and Herman Schultz attending the funerals of the fallen members of the Sinister Six, using his money to provide for the people they left behind.