think of falco/fox/falcon/etc in smash as the ryu/ken/chunli of street fighter. for dozens of installments of street fighter those characters (among others) have developed a formula and playstyle which became the canon of their games. how can you imagine ken without his hadouken, sure they added new things overtime, but their base gameplay was still there. sf4 even preserved some of the subtle glitches (kara grabbing i believe was the name) which gave those characters that edge. they could have went ahead and reimagined the characters, but since they knew they filled their own niches and became so iconic, they went with not tampering them.
the same is true of our spacies and other high tiers, their playstyles have become the canon and basis of the smash bros melee scene. by changing around these top characters, characters that have proven to work and play well and have weaknesses and strengths that balance them out, we would be undermining the whole project. without fox falco falcon etc in their forms from melee, we wouldn't have anything to base our balancing methods off of, we wouldn't have anything to compare them to. brawl falco may have had a bunch of stuff given to him in brawl, but it was much too alien, and falco's playstyle, if not presence was so integral to melee. granted we could start over again, but those characters provide enjoyable experiences that have stood the test of time, and have thus become staples of the smash bros melee genre.