I think that the Mandalorians resember the USMC because of the Core Values the USMC has, like Courage, Honor, and Commitment, "which forms the bedrock of their character. It gives them strength and regulate their behavior".
The Mandalorians seem to abide by these exact code of honor. They're brave and have camadarie. They even seem to act the same way as Marines. I know the Spartans have a code of honor, as well, but I dunno what they exactly are.
Their leadership traits also seem the same.
Bearing, Courage, Decisiveness, Dependability, Endurance, Enthusiasm, Initiative, Integrity, Judgement, Justice, Knowledge, Loyalty, Tact, and Unselfishness make up the USMC leadership traits. Remember when that one Mandalorian in KOTOR 1 who challenged Canderous to a duel because Canderous abandoned some men or something?