>>45662304Some of them are just because they were easy clones, those being Lucina and Chrom(populr characters both, though).
Some are to represent/advertise newer games, like Robin, Byleth and Corrin.
Roy was both back in Melee, but came back with a less clone-y moveset because he was a popular veteran.
Ike is funny because Sakurai actually just designed a "heavy swordsman" moveset and needed a character to use it, so he asked the FE team if they had someone suitable, and they suggested Ike.