Let's be honest, Fox would have cancelled this show after five episodes if that. CW will keep it on air for ten years or more... and is more in line with the demographic they're shooting for. From Archie Comics:

Just announced at Comic-Con International: San Diego 2015, Archie Comics released major details about the upcoming "Riverdale" live-action series.

Originally developed for FOX, “Riverdale”—a dark, twisty, one-hour drama based on the iconic “Archie” comic book characters, including Archie, Betty, and Veronica, as well as Josie and the Pussycats—is now set-up at The CW network, with the key players remaining the same: Warner Brothers is the studio, THE FLASH and ARROW chief Greg Berlanti is producing and Roberto Aguirre-Sacasa, Archie's Chief Creative Officer, is writing the pilot.

"The CW is a perfect for for the vibe and tone of the Riverdale series," said Archie Comics CEO/Publisher, Jon Goldwater. "We couldn't be in better hands. Working with WB, Greg Berlanti and having Roberto involved has made this a dream project come to life. This is a major, major thing for this company."

As fans know, Aguirre-Sacasa is also the mastermind behind Archie's two bestselling and acclaimed horror titles, AFTERLIFE WITH ARCHIE and CHILLING ADVENTURES OF SABRINA. He is also a consulting producer on the “Supergirl” series.

The "Riverdale" news comes hot on the heels of the hugely successful sellout Archie relaunch, kicked off by a stellar debut issue from the powerhouse creative team of writer Mark Waid and artist Fiona Staples, which has been the buzz of this year's Comic-Con.