Commandments between man and man, like giving charity, do not have a blessing associated with them. The language of blessings is "Who has commanded us", meaning the Jews. Because non-Jews also do acts of kindness to their fellow man as humanitarian acts, we do not make a blessing that would infer that we as Jews have exclusivity as far as the acts between man and man.

Heard from Rabbi Shafran Shabbos Parshas Mishpatim.