Because the people there don't wanna be invaded, like at the goldenrod radio tower.
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To do it in johto just get the card thingy after you get 7 badges but in kanto you cant
No but you can go to kanto but you can own sinnoh pokemon.you cant
You need a special card to connect your radio to kanto's radio frequencies.
you cant
You beat the seventh gym leader then go get the team rocket costume from in the tunnel in Goldenrod then you go beat teamrocket in the tower. The elevator will not work unless you have rotom though.