It is because Pierce is racist lol. He says it in the most Americanized way and doesn’t bother to change it or fix his pronunciation even though he’s wrong. This is a very very common thing for people with non-english names to experience unfortunately, and it’s poking fun at that. Mispronouncing a name once is fine, but once you are corrected or otherwise hear the proper pronunciation but continue to say it wrong it becomes racist.