どうして紳士らしくふるまおうとしないのか。

why?; for what reason; how; in what way; for what purpose; what for

gentleman

seeming ... (expresses judgment based on evidence, reason or trustworthy hearsay); appearing ...; -ish; like a ...; typical of ...; appropriate for ...; becoming of ...; worthy of the name ...

to behave; to conduct oneself; to entertain; to treat someone (to a drink); to make tea for someone (tea ceremony)

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

to do; to cause to become; to make (into); to turn (into); to serve as; to act as; to work as; to wear (clothes, a facial expression, etc.); to judge as being; to view as being; to think of as; to treat as; to use as; to decide on; to choose; to be sensed (of a smell, noise, etc.); to be (in a state, condition, etc.); to be worth; to cost; to pass (of time); to elapse; verbalizing suffix (applies to nouns noted in this dictionary with the part of speech "vs"); creates a humble verb (after a noun prefixed with "o" or "go"); to be just about to; to be just starting to; to try to; to attempt to

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way