From what I gather from his Wikipedia page, essentially, his contract with WWF ran out and he chose to go back to WCW. Also, from the show last night, Ric is the "old school" NWA-WCW type, and Ric's character was more suited to WCW than WWF (WWF, especially in the 1980s and early '90s, was extremely "cartoony", while WCW's characters were much more real and edgy. It's actually why during the Monday Night Wars I was more of a WCW fan than WWF). The whole reason why Ric left WCW in the first place was "creative differences" - one of the bookers wanted him to shave his hair, alter his image, and become a guy named Spartacus, and when Ric refused he was fired. I'm guessing at the minimum hatchets were buried, although it wouldn't surprise me if axes were dropped on a certain creative team member that decided to come up with that stupid Spartacus gimmick for Ric and then promptly fired him when Ric didn't want to do it. Talk about one of your all-time bonehead moves - firing perhaps the biggest name on your roster because you decided you wanted to kill his money-making gimmick.
It's really interesting you bring up WCW signing WWF's aging talent and the major boost they gained from it in the mid-to-late '90s. While it's absolutely true, it's also what ultimately killed them in the end. Big-time money contracts that WCW really couldn't afford (to the point where much of those names were actually signed directly to the parent company AOL-Time-Warner), but also they gave those guys absolute creative control, and instead of using that power to make the product better and develop the future generation of stars, they used that power to keep themselves at the top and bury the younger talent down the card - all major reasons why Chris Jericho, Chris Benoit, Eddie Guerrero, Dean Malenko, Perry Saturn, and perhaps others I'm blanking on defected from WCW to WWF.