It is quite obvious. Marvel wanted its own Spider-man so that they could build a cohesive animated universe just like their cinematic universe. they did it by negotiating with Sony and convincing them to relinquish all television rights to Spider-Man, including animation, in exchange for "some concession vis-a-vis the live action Spider-Man features".They also wanted to use Spider-man's popularity (esp. in animation) to promote their second and third rate characters like the way they did with the Marvel Team-Up comics in the 70's. So as the result, Spectacular Spider-Man was canceled unceremoniously to make room for Marvel's new cool Spidey animated series and the fans are left with a kid-friendly Ultimate Spider-man cartoon and a crappy-looking Amazing Spider-Man live action film (thanks to that aforesaid "concession")