I don't get this. Why do people expect Lucas cut and Falco ok? Falco is just as much a clone as Lucas. Personally, I don't want or expect either to be cut.
Partially because Falco has seniority.
Partially because Lucas's one and only appearance was in a Japan only game.
Partially because MOTHER is finished, though Lucas detractors usually use the word "dead franchise" instead.
Partially because Falco is more popular than Lucas.
Partially because Star Fox is bigger than MOTHER.
Some or all of the above reasons. As for me, I want both of them in. While I don't personally use Falco, the backlash for his removal would be ridiculous, and MOTHER 3 is an amazing game and everyone who hasn't played it should. I don't use Lucas as much as I used to, but it would be sad seeing him gone.