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So then why did "Team Rocket's radio show for adults" exist?
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It wasn't really "for adults", that's Bulbagarden nonsense. It was on in the early afternoon, it got advertised on Pokemon Smash... it may have been written at a somewhat more "hey, older fans are going to listen to this" level than the anime is, but it wasn't "a show for adults".
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And judging from Mima's scripts for it, particularly the first episode, it's not an unfair thing to say that there was hatred for BW within the staff.
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It also played directly into the ongoing anime plot, it was likely already decided at the time that the Rocket trio would go back to their original selves, and... well, they needed to use the characters' original personalities for the radio show. It wouldn't work otherwise. It's a comedy show, you need funny hosts with outgoing personalities, not dead-serious agents.
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Not only is the show static, the long-term ratings don't really reflect any real change when things do happen. That tells me that Team Rocket in BW actually weren't affecting the ratings in any significant way.
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The writers' job is to catch the audience's response to their show before it starts affecting ratings. The show is big business, they want as many viewers as they can to watch.
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And the merchandise sells no matter what they do.
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The anime is an important part of the franchise's advertisement. If kids keep watching, they won't lose interest in the franchise, and will keep wanting new plushies and toys and mugs and games and whatnot. The anime also does a lot of advertising for specific things Gamefreak wants advertised at the moment. N showed up in the anime alongside a lot of N merchandise, the Milos arc aired at the same time as a set of kami trio merchandise appeared, etc. The anime is very important to Gamefreak.