One good reason: if they don't make the movie, the rights to a hugely popular franchise revert back to their biggest rival company.
#1 reason for Sony. (It's likely to finish around $750 million worldwide.)
Oh, I know, but there's a difference between making a movie to tell a story or to get a point across, and making one just to make money.
Please, give me one good reason WHY Spider-Man needed a re-boot in the same decade as Raimi's trilogy. However, since they did do it, they at least owe it to Spider-Man fans to do it right. Sony only had one thing in mind when making that shit stain of a movie.
In a way, yes, it was about money due to their rights to the character requiring a release by 2012 to continue the contract. Clearly, the Raimi trilogy did not age well. Fans want a respectable adaptation of the character, and that demand is not going to dwindle over time. It hardly matters if they made it 10, 15 or 20 years after Spider-Man 3, the money will be there.
If they really didn't care about the story, they wouldn't have cancelled Raimi's attempts to make Spider-Man 4. They got pretty deep into that pre-production with John Malkovich negotiating to play The Vulture and Anne Hathaway playing Felicia Hardy. Would she turn into the classic Black Cat? NOPE. She would've turned into The Vulturess. Despite this shit-brained idea, the movie probably still would've turned a solid profit on name alone.
Thankfully, Sony pulled the plug on it to give Spidey new life. You cannot tell me that that shitty idea would've been better for the character than The Amazing Spider-Man. Is The Amazing Spider-Man perfect? Hardly. However, the franchise is at least set to build off this and its inevitable retelling of the origin to sequels that are closer in tone and characterization of Spider-Man from the comics.