The company recognises it needs to go in a new direction to best push the strengths off it's top star.
The WWE pushes a new top star/combined with the old star stepping down(moving on).
The new top star's different characteristics require the company to restructure it's style.
(Bearing in mind, that even when different wrestlers hold the title, WWE still sees that one guy as the true headliner).
Hulk Hogan leaves WWF (classic era).
Larger-than-life, charismatic big man, (virtually) undefeatable babyface.
Bret Hart becomes the face of the company (New Generation). Bringing an athletic/realistic wrestling style. Often plays the brains over brawn outwitting an opponent.
Steve Austin headlines the WWF, and leads to the Attitude Era. As defined by Austin's character.
Brawling, violent, edgy, controversial, large promo segments.
Brock Lesnar moving to John Cena, gives us Ruthless Aggression era.
Strongman, hard-hitting wrestling with less flair.
PG Era due to Linda McMahon running for the Senate election in Connecticut. She began campaigning properly in 2009, so the groundwork started in 2008 when WWE became PG.
A very bland product, where very little changes, week-by-week/month-by-month, 50/50 booking, jeering by the crowd to entertain themselves.