Color me as someone who is still completely in the dark as to why having multiple versions of D&D in the world is a bad thing for WotC or the marketplace. No one has been able to articulate a satisfactory reason why.
The reasons given are either entirely personal to that particular player...
...either they do not want to have to spend more money to buy a new game, or
...they can't find people to play their preferred version of D&D because everyone around them are switching to a new edition.
But neither of those reasons have any bearing on WotC or the marketplace. Because in the first instance... it means WotC's already gotten money from that person previously, and there will always be someone else to try the game or return to the game to take that person's place... and in the second instance... it means that they're making money off of all the people around that person who just don't care that it's a new edition they are switching to, and want to play it anyway.
Or the other reason given by the people is that it "splits the gaming community".
But so what? The RPG audience has always been split. For decades. Across all manner of RPGs. It's nothing new. It's nothing to fear. But for some reason... when we point out that there's a goodly amount of gamers out there who are exclusive to Shadowrun, or World of Darkness, or GURPS, or any other game, and they don't play D&D AT ALL... it's no big deal. But as soon as it gets mentioned that players are playing any other edition of D&D, all of a sudden it's for whom the bell tolls. It's the downfall of the game. As though the only way for D&D to survive is we all sit in one big, happy D&D circle playing the same single edition forever and ever and ever. I mean hell... how many more people do we need to see on these boards make the completely unfounded claim that if the new edition of D&D "doesn't sell", then Hasbro's going to put it on the shelf for a decade? That's a complete bullcrap statement with no basis in actual fact... made by a person who has no knowledge of the situation and is saying it merely because they themselves don't want to buy a new game, and this kind of ridiculous hyperbole is the only way they can attempt to get across to WotC that "they mean it!" They're serious! Don't make a new game, cause they're not gonna buy it!
But nobody over there cares. Because others will. They always will. They will buy a new game. They might not play that same game for 30+ years like some people out there to with like AD&D... or heck, might not play it at all after buying it. But it doesn't matter. Because people buy it anyway. Because believe it or not... buying roleplaying games is fun. Reading roleplaying games is fun. Playing roleplaying games is fun. And even though some people have a stick up their butt about seeing a new D&D take over the public's consciousness from their precious, preferred version... doesn't mean WotC's going to change their publishing methods to keep those people happy. Not when the rest of the "gaming community" is right there to pick up that person's slack.