There are too few Heavyweights on both brands. I remember in the
Attitude Era there would be at least 4 gunning for the championship
at any given time. They didn't have matches like: "Batista vs King
Booker", & "Edge vs Cena" for PPVs. Those are one-on-one
matches, more fit for normal nights on RAW and Smackdown!. PPVs are
meant to be special.
They had matches like "Fatal Four Way - A McMahon In Every Corner"
involving The Rock, Triple H, Big Show, and Mick Foley. Not to
mention the "6 Man Hell in a Cell Match" involving The Rock, Kurt
Angle, Austin, Triple H, Undertaker, and Rikishi.
Could be because the Monday Night wars are over. So, the shows were
more lackluster because there was nobody to compete with anymore,
since WCW was run into the ground, and ECW was revived under WWE,
and thus he could finally relax. Who's going to beat him? TNA? Nah.
ROH? Nah. CZW? Hell no...
Vince McMahon was concerned by the injuries that had accumulated
during the Monday Night Wars due to the promotions becoming edgy
with their storylines, and thus forcing many wrestlers to execute
more and more dangerous maneuvers and plot points (Owen Hart and
his tragic death). Also, the addition of the luchadore talent from
the purchased WCW added dangerous high flying maneuvers to the
WWE's repetoire. Finally, McMahon realized that, with his owning a
practical monopoly on wrestling, a wrestler's union could quickly
form if wrestlers became uneasy with the WWE's demands, could thus
topple the company.
All these factors led McMahon to issue orders to deliberately slow
down the pace of matches. He also barred many dangerous maneuvers
that had become commonplace, such as the 450 splash and any and all
piledrivers, despite the fact that the moves were popular with fans
(also, McMahon destroyed the popular Hardcore Title). These acts
were done to prevent injuries (thus protecting McMahon's
investment), to prevent wrestlers from complaining about injuries
and danger (thus preventing union activities), and because McMahon
did not need to produce as entertaining shows anymore (because he
had a monopoly).