Wrong on several different levels as usual.
First off, the Bengals made the Super Bowl in 1981 under Forrest Gregg, not Wyche. You make it seem as if Wyche made the Super Bowl twice with the same group of players. He didn't. In fact, I would guess that only Munoz, Collinsworth, and Jim Breech played on both the 1981 and 1988 Bengal Super Bowl teams.
Second, if you take a closer look, you can see why the Bengals were one-year wonders during their Super Bowl seasons.
The Bengals had basically sucked from 1977-1980. But they were a young team in 1980, and they added Cris Collinsworth in 1981 along with a couple other guys and became really good. 1981 was also a season when the "old guard" like the Steelers, Oilers, Rams, and Vikings went downhill. The Bengals filled the void. There defense was never really that good, but it was good enough in 1981. The Bengals were still pretty good in 1982, but RB Pete Johnson started getting into cocaine, and their defense never got better. By 1983 the Bengals were back to their losing ways. Pete Johnson was gone, a few key players were signed by the USFL, Ken Anderson had lost his mobility, etc.
Sam Wyche took over in 1984, and while they were sometimes exciting, they never made the playoffs. Wyche should have been fired in 1987 (4-11), but the Bengals gave him one more year, probably due to their cheapness. Can you imagine an NFL coach being with a team for 4 seasons, never making the playoffs, going 4-11, and keeping his job for a 5th season??
The Bengals probably underachieved during Wyche's tenure; they had some really good players. In 1988, Icky Woods was added to the team at RB and he really helped control the ball. Young defensive players like Tim Krumrie and David Fulcher were now in their prime, and the Bengals offense, which was always pretty good even in losing years, exploded with the addition of Woods. But in 1989 the Bengals fell back to mediocrity, and in 1991 (Wyche's last year) the Bengals had become the worst team in the NFL. Why? After 1988 Icky Woods got fat on success and was never the same. Collinsworth retired. Tim Krumrie broke his leg and was a shell of himself. James Brooks got old and was never replaced. Too many key players had drops in performance and the Bengals had no depth.