From 1992 through 1995, the Dallas Cowboys went 49-15 in the regular season and 10-1 in the post-season. When they won their third Super Bowl in four seasons in 1995, Troy Aikman was 29, Emmitt Smith was 26, and Michael Irvin was 29.
The Cowboys won one more playoff game in 1996, and haven't won a playoff game since.
What happened? Why couldn't a team with young superstars that was so dominant for four seasons maintain its dominance?
The answer is simple: they failed to continue to add talent through the draft.
The 1992, 1993, and 1995 Super Bowl teams featured many Pro Bowlers that were Dallas draft picks: Troy Aikman ('89), Emmitt Smith ('90), Michael Irvin ('88), Mark Stepnoski ('89), Erik Williams ('91), Russell Maryland ('91), Ken Norton ('88), Larry Allen ('94), and Darren Woodson ('92) were all Cowboy draft picks that made at least one Pro Bowl during a Cowboy Super Bowl season. Dallas built its championship nucleus successfully through the draft.
However, after 1995, the Cowboys generally failed to draft Pro Bowl quality players. 1997 draft pick Dexter Coakley made Pro Bowls in '99, '01, and '03. 1998 draft pick Flozell Adams made Pro Bowls in '03, '04, and '06 (after Aikman, Smith, and Irvin were all gone). No other Cowboy draft picks from 1995 through 2001 made a Pro Bowl while playing for the Cowboys.
Dallas dominated from 1992 through 1995. They were good from 1991-1999, when they made the playoffs eight of nine seasons, but they really only maintained a level of superiority for four seasons. In pro football, it appears hard to maintain dominance with the same nucleus for too much longer than that. The Packers won five championships over a seven year period from 1961 to 1967, largely with the same nucleus. The Steelers won four championships over six years from 1974 to 1979, again largely with the same nucleus. As I discussed previously, the San Francisco 49ers were able to maintain dominance longer (four championships in nine years from '81 to '89, five championships in 14 years from '81 to '94) because they consistently added quality football players through the draft.
The Dallas Cowboys built a dominant team through the draft, but failed to maintain a dominant team through the draft.