The Meaning of Life, the Universe, and Everything.
This is more or less a theory I have, that the version selection option tab split up, and continues to split up, the Minecraft community. I say this because of the option it gives, for players to stay behind the newest updates because they just don't like the latest version's changes. Of course, there are logical reasons to stay behind, such as to get access to mods that have been abandoned and left stuck on that version, but sadly I don't think many people use it for that. I feel like I'm seeing a lot of players use it just to avoid change, which splits up the community into like 4 or 5+ different types. As much as I hate to say it, being someone who mainly sticks to 1.7.10 and 1.8, I feel as though this option just never allows the community the game has to progress. Sure, the newest updates may bring in new players, but the old ones who never allow change will still be there, sometimes harassing the newer players and acting like old people saying things like "Well back in the original version of..." Now please keep in mind I'm not saying everyone is like this. As I said, there are logical reasons for this option and even mature players who keep personal preference in mind, I just feel like their in the minority though.
As somebody who has never updated past 1.6.4 (link in signature) and has probably spent less than 3-4 hours in total on newer versions (an average play session; by "never updated" I mean normal gameplay) I don't see how this has really affected the community as much as, say, all the new Minecraft editions; for the most part 1.6.4 is the same game as 1.12.2 and the gameplay is mostly the same (if I mention some game mechanic most will know what I'm talking about; likewise, much of what I know about how something works in 1.6.4 applies to the latest version), just with some new features and some old ones removed; the differences would mainly affect multiplayer since you have to use a specific version to play on a server (which are mainly about minigames these days, which are less affected by version changes) and I've never played multiplayer, and singleplayer is more popular in general.
Also, while I have made a mod that adds in some newer features, much of my playtime, and playstyle, has been in what is essentially vanilla 1.6.4 (a few minor mods) simply because those newer features are not "must-haves" for me (aside from Mending, and only because Mojang removed the feature where renaming an item would keep its cost from increasing, so they more or less cancel out) and I would not use them even if they were in the game by default (as it is I don't use many features present in 1.6.4, such as redstone (not counting basic railways or a button by a door), or horses; much of what I do when playing could be done in Classic, the first version to have caves, mobs, ores, tools, and Survival mode; not that that means that I'd prefer that version over the latest versions since there are other features that I would not want to give up).
I also get a very strong impression that I am the exception, not the norm; for example, consider how unknown my namesake mod is despite having been around for over three and a half years with semi-regular updates - 7 results on Google? Even those sites that love to steal and repost mods have ignored it (it adds in some newer features and there is a semi-popular mod for 1.7.10 (20,700 results) that adds 1.8+ features to that version so this likely shows just how few still play 1.6.4; 1.7.10 is mainly still popular due to mods and even then many mods, including big ones, are being updated so its days are numbered. Yes, some people still play even older versions, like 1.2.5 for Tekkit Classic, but they are very rare.