I am not certain if 3.5 and Pathfinder are still more popular than 5e, since I have not seen any stats for 2016. To be honest, they probably probably are not: from what I've seen (anecdotes, but who cares), 5e has caught on. However, there are still a significant number of people who prefer 3.5 or Pathfinder over 5e, and I do not think that it is because they're unwilling to change. "Resistant to change" has always been a slur from those who like newer things at those who like older things, and it is hardly ever true. After all, people who play RPGs also do other things that are much more different than switching from one RPG to another. If they stick to one tabletop RPG, they always have reasons for doing so.
For me, 5e is okay and I can get behind some of the ideas in it. However, I prefer 3.5's skill system, feats and magic, and I've never been fond of advantage/disadvantage as a mechanic, or of 5e's proficiency system. Furthermore it would take years for 5e to have the breadth of content that 3.5 players enjoy, and I don't think WotC even wants to do that.
On top of that, any new game has to compete not only with the printed version of an older game, but also with all the mods people made to it. Too much has been made of the so-called Oberoni Fallacy; I think "it can be houseruled" is a valid answer because people do houserule, and some things are easier to change than others. Edition wars are pointless because there is no way to compare two games until you sit at one another's table and see how they play the game, not just compare books. This does not only cover houserules, either: the handbooks on this board, Giant in the Playground, and the late WotC boards all affect how D&D is played, as people can obtain "system mastery" quickly and without cost.
In the digital era, it is hard to track what is most popular. Book sales can no longer be used to track a game's spread, because Pathfinder is almost entirely given away for free with its SRD. 3.5 gets similar treatment with D&Dtools, 4e has its character builder, and for any game (D&D or otherwise) the number of pirates exceeds the number of book buyers. A way to stat games is to track which are played online using the virtual tabletops and hope it is a representative sample. Apart from that, I don't know. But I do know that each edition has its own fans and, instead of reuniting the fanbase, 5e has created just another branch.
There's stolid and austere OSR, with its limited rules and distinct playstyle. There's the constantly-morphing chimera of AD&D, with its disunited mechanics and decades-long hodgepodge experimentation. There's the gargantuan 3.PF, with relentless growth built around a single core mechanic. There's firm and dependable 4e, with its separation between fluff and mechanics and its single pattern. And now there's 5e, with some of the limits of OSR with some of the style of 3.PF, forging its own path for those that want an easy-to learn fantasy game with heroic scope. The winner is the player, the loser is anybody who hopes to make money off this industry where the niches are too small and every purchase is an act of charity.