Sometime in the 1970s:
"Okay, so we're bringing back the Jetsons."
"Right."
"And maybe we do it like the family's growing up a little. Like Judy's an adult with a job as reporter or Elroy's doing teenager stuff now."
"Oh, yeah, that'd be cool. Fans of the original show might really get a kick out of that."
"HEY, YOU KNOW WHAT'S HOT RIGHT NOW? THE PARTRIDGE FAMILY."
"Okay? But our job is to do a Jetsons revival."
"YEAH, NO. I TOTALLY GET THAT BUT HEAR ME OUT--"
And that's apparently pretty much how it happened, give or take a few details:
https://en.wikipedia.org/wiki/Partridge_Family_2200_A.D.