Why did Eliezer tell them about the oath that Avraham had made him swear?
Rashbam: To inform them that it was not because of a lack of women of Kena'an, but because he despised the Kena'aniyos and because he preferred those of his family.
Above (Pasuk 3), Avraham said "Asher Anochi Yoshev b'Kirbo." Why did Eliezer say here "Asher Anochi Yoshev b'Artzo"?
Hadar Zekenim, Riva: Avraham could say b'Kirbo (which connotes that it is his land), for Hashem promised it to him. Eliezer feared to say it, lest they rebuff him - "veha'Kena'ani Az ba'Aretz"!
Malbim: He intended, even though I live in their land, and they should have precedence over girls of my homeland, still, my family has precedence due to kinship.
Ha'Emek Davar: He does not forbid only those near him, rather, all girls in Eretz Kena'an. Eliezer made them think that the Shevu'ah was due to adamancy about Benos Kena'an. Rather, it was due to suspicion lest Eliezer take a nearby girl, to spare himself toil (refer to 24:3:6:4).