Because of having too much interest in small and unimportant matters: Petty, paltry, trifling, trivial apply to something that is so insignificant as to be almost unworthy of notice The meaning of petty is having secondary rank or importance
Bettie Page & June King : vgb
How to use petty in a sentence.
Of little or no importance
Of lesser importance or merit Having or showing narrow ideas, interests, etc. If you describe someone's behaviour as petty, you mean that they care too much about small, unimportant things and perhaps that they are unnecessarily unkind. Definition of petty adjective in oxford advanced learner's dictionary
Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more. The adjective is derived from middle english peti, pety (“little, small Insignificant”) (modern french petit), [2] ultimately of imitative origin.