Wrong, Many characters do fight the respective evil teams.
Champion Lance does face off team rocket, and team rocket aligned merchants.
Champion Steven does face off with team aqua and team magma.
Gen 4 has Looker being a character to arrest evil teams after their plans have been thwarted, although he never really fought them.
Gen 5 has the most characters who have outright been fighting Team Plasma.
All 8 Gym Leaders, The champion, Hugh, the b2w2 rival, Looker again, Even former Plasma members fought Neo Plasma.
Gen 6's story was so rushed, that no one probably knew what team flare was trying to do.
Gen 7's Team skull , Aether Foundation and Ultra Recon Squad are self contained groups that never really got much attention from many characters.
Gen 8's Team were just fanboys and fangirls who occasionally hindered others, but never really fought anyone other than the main character and the rival.
Team Rocket pretty much owned cities until protagonist and Champion got involved.
Team Aqua and Magma fought each other often, but Champion and protagonist stopped them.
Looker wasn't much of a fighter, and Cyntha only investigated as well.
Gen 5 was the real last generation where the whole region in some form were affected by the team that many people had to face off with them.
