I can rationalize after the fact why the Japanese like it. They 'romanticize,' if you will, the English character set not so much because they're romanticizing Americans, but that it's a foreign character set and looks cool.
Pokemon card game is a good example. "HP" is in English, several attack names will include English words, etc. It looks foreign and thus cool.
But so too is French foreign and looks cool. Since it's not so much about being English, rather that it isn't Japanese, which one it is in particular is essentially irrelevant. They can mash character sets together and it's fine.
What I really don't understand is why it's used in North American marketing. In fact, it's probably where it originated, and not in Japan. It would've made more sense to call it "Pocket Monsters," but I suppose some marketing guru decided it was too many syllables and not marketable enough. The é really is not a marketing pro in the US; perhaps at a time when anime and Japanese culture really was starting to noticeably gain traction in nerd communities in the 90s, someone had advised them on trying to more exactly mimic Japanese phonetics, assuming people were about to start adding diacritic marks when 'adapting' Japanese marks, rather than, e.g. picking between either Lugia or Rugia and calling it a day.
It was anticipatory in the event of a language adaption reform that never ended up taking off. There's no real rationale to use é for English language marketing, the English language makes up rules on pronounciation on the fly – e.g. "kernel" for colonel. Hell, look at "Arceus". The TPCi pronunciation is incorrect. No one actually cares.
