This subject here isn't as easy to pinpoint as the other things on this list. Probably the best place to look at was the Fingerpoke of Doom incident, there WCW showed not only its fans, but also the wrestlers in the back, that WCW was there to push its older stars and if you didn't like it, too bad. There was another moment that will be forever engrained in every fans memories as they saw Hogan poke Kevin Nash in the chest, Nash take a comically gigantic bump, Hogan pin Nash to become champ, and the NWO factions reunited. Then the only wrestler that WCW actively pushed and allowed to get over with the fans during that period, Goldberg, rushed to the ring only to get beat down, made mortal before the fans' eyes.
Now when people talk about "old" vs. "young" stars it's not about their actual age but rather their TV age, or how much fans have seen them in the main event scene or in the same feuds over and over again. Hogan, Nash, and the NWO in general had become incredibly stale at that point, yet WCW felt the need to keep them at the forefront while cutting "younger" stars down at the knees.
These guys would become frustrated and eventually join the WWE in their own time throughout different times in WCW history before and after the NWO, yes, but still due to being held down in favor of the old gaurd. See if you recognize any of these names: Steve Austin, Triple H, Chris Jericho, Eddie Guerrero, Rey Mysterio, the Undertaker, Chris Benoit. These were just a few of the guys that found fame and fortune in the WWE because the WWE saw the potential in them and allowed them to grow into main event wrestlers and all of whom listed here eventually became world champion, some on multiple occasions.
If WCW realized the talent that they had and pushed these wrestlers accordingly, there would have been quite a difference in the wrestling landscape which leads to the next slide.