Why is Frenchman seen as an acceptable term but Chinaman is not?

Historically, the Word Chinaman was used a slur as well as a description of Chinese people. Frenchman never had a derisive use. As a result, Chinaman has come to be emblematic of the Anti-Chinese sentiment that prevailed in the US and Europe in the 19th century and is considered racist on those grounds. (It is the same reason why "Negro" is no longer acceptable to refer to Black individuals.)