Here's why:
* The current Spider-Man franchise is separate from the one James Franco was in. The current films, starring Tom Holland, are part of the Marvel Cinematic Universe (MCU).
* Franco played Harry Osborn in the Sam Raimi Spider-Man trilogy. Those films ended in 2007, and there are no plans for a direct continuation of that series.
* There have been rumors of a possible "Spider-Man 4" with Tobey Maguire, but nothing concrete has been announced, and it's uncertain if James Franco would be involved.
Therefore, it's highly unlikely that James Franco will appear in any future Spider-Man movies at this time.