Are they? Where are you pulling these numbers from? If we're going to pull out numbers, let's say the Melee scene that enters tournaments (the ones that actually play in tournament) is numbered at (and I'll be generous here) and say it's 30,000 people world wide that are currently active in the Melee tournament scene.
Compare that to the world wide sales of Melee at 7 Mil units, now let's go ahead and assume that the majority of those people don't play Melee as much as they did in the past and we'll take off a considerable chunk.
So I'll go super low and assume that with emulators and copies owned, about 100,000 people worldwide will still play Melee every now and then either via their Wii or Dolphin or Nintendont, that aren't actively playing in the tournament scene.
Just from that rough and (obviously inaccurate) comparison, the competitive scene is still low.
Now let's forget everything I just said as hoopla and think about it like this, if Melee had multi million sales, and they release a new one, how many of those casual players are going to come back? A lot, the same thing that happened with Pokemon when it got rereleased, or the same thing when Mario Advance series happened. Let's say the competitive scene goes "Meh, I don't want this it has changes!" that's such a small loss of sales vs the potential of new people and old casuals returning that it isn't worth dedicating 100% to. I'm not saying don't dedicate any, but 100% is pushing it IMO.
Now on to the "casuals", they get to revisit the past, and what would entice these people more are some changes, something to add some freshness to that past. At the same time, newer people, a younger generation will be able to be introduced, and let's say a kid wants to play Mr. Game and Watch and his shield sucks, it'll deter the fun for that person, or they wanna play Kirby but their friend keeps jumping out of their throw, once again, it'll deter the fun. Even if these are minority examples, it still is something that would only make the game better and shouldn't be shunned.
Are simple fixes like these truly detrimental to the competitive side? Can't we like come to a middleground here for the sake of the game itself? There's nothing to "lose" by changes like these.