GameFreak loves to screw with everybody.

[Pyro]

From TVTropes:

Spoiler: PLOT DETAILS

No Fair Cheating: If you use a Walk Through Walls cheat on the Plasma Frigate to avoid entering the password or disabling the force fields, once you reach Colress' room, he will have the team he uses after you've beaten the Elite Four and Champion full of Level 72+ Pokemon. And you're more than likely gonna get slaughtered.

 

[Pandapowah]

The person will most likely use another cheat that powers up their Pokemon.

 

[Time Turner]

There's actually a lot more examples.

 

[User4042]

From TVTropes:

Spoiler: PLOT DETAILS

No Fair Cheating: If you use a Walk Through Walls cheat on the Plasma Frigate to avoid entering the password or disabling the force fields, once you reach Colress' room, he will have the team he uses after you've beaten the Elite Four and Champion full of Level 72+ Pokemon. And you're more than likely gonna get slaughtered.

maybe thats why there arent any actionreplay codes for it