Lol, fine, I'll explain the analogy. Melee is very impressive to watch, and high level competitive play tends to draw in people to want to play the game too. After playing it for an hour though, it should be blatantly obvious how difficult the game is at first attempt. It takes hours of dedication to learn the tech and apply it properly, then it takes a ton of work to learn the very complicated matchups. But it's very rewarding to do so and the end result is a **** experience.
B+ is bright, shiny, and relatively simple. It draws people in because it's relatively so much EASIER to control your character. You skip all of that tech skill grinding and matchup research (matchups in Brawl/+ are pretty lol compared to the ones in Melee), and get right to the actual game part. You don't forget how to play, there isn't much to remember, and it's just plain fun to play.
EDIT: Both are competitively viable because they include the fundamentals of all the Smash games, things like spacing, mindgames/prediction, approaching, DI, etc.