The problem with SWTOR is simply that it literally made every mistake it wasn't supposed to. The WoW-killer might appear, or simply a game that will replace WoW, but in order for that to happen it pretty much has to do everything that SWTOR was going to be in the minds of it's fans and what it's devs implied.
A lot of the predictions for TOR wwere based around the information that it was pretty much the "Avatar" of MMO projects, with close to a billion dollars being fed into this thing. In reality the amount of funding it had was considerably more modest, which also meant that it wasn't going to meet the heights of what was possible, and be more along the lines of what we'd expect from a "normal" high budget game.
Among the first things the fans were asking is what was the endgame going to be like, EA played it coy, but implied it was going to be huge. As a result when people played the game and found out we had a typical (ie very weak) endgame that was pretty much it's death knell as any kind of wow-like phenomena. It's very true that WoW didn't have a huge endgame when it first started, but at the same time it wan't really competing with anyone else that did either, where games coming up now are competing with WoW. Developers constantly fail to learn from their mistakes, and EA/Bioware pretty much jumped into the same pit as everyone else. People are going to play through any amount of content and hit whatever the "top" is for a character pretty quickly, the make or break point for people is being able to keep those players motivated to play their top level characters and re-upping subscriptions in order to do so.
I'll also go so far as to say that probably 99% of the problem is casual gamers and deciding to cater to them. The problem with a robust endgame is that casual players will QQ that they don't think it's fair that they won't be able to get the phattest lewts and biggest rewards without putting in a huge amount of time and effort, and actually having to become skilled at the game. By making a game where casuals can acheive the lofty heights of power, you kind of removed a lot of the motivation from the other players, assuming there was much content for them, which there typically isn't.
Likewise a lot of the "streamlining" is kind of counter productive. A point a lot of people miss is that while the "old school" 40 man raids meant that not many people could raid because of the time, committment, and organization, it means that you wound up with a VERY dedicated base of people who kept reupping their subscriptions just so they could raid once or twice a week. Something that gave WoW a solid, core audience during it's most pivotal times of development. It had the benefit of having sprung off of that kind of thing, to add/change things in a more casual direction to get the best of both worlds.
Most people become attached to one or two characters, if when you max them out all you really have to do is use the game as a glorifed chat client, and hang out on a space station waiting for queues or groups.. groups which can zerg most of the content (though admittedly not all of it), your going to lose a lot of people, your certainly not going to keep enough to get the kind of mainstream uber-success ToR was angling for.