1)
Why does the Navi record that he cut off the thumbs and big toes of 70 kings?
1.
Rashi: This teaches the greatness and wealth of the kings of Kena'an. Adoni Bezek was not worthy to be called among Malchei Kena'an (even though he was so powerful)!
2)
Why did they take him to Yerushalayim?
1.
Rashi: That was the next city they would fight against.