Actually there's quite a few reasons that there's little competition to Second Life in existance or planned - at least the sort of competition that a Second Life user would think of as a competitor to Second Life (hint: They don't think TSO is, or Kaneva, or Red Light Center, or Project Entropia or IMVU. Many don't count Active Worlds or There as competition either).
One of those reasons is that even people who think they're in the same industry or who are pundits and commentators on the industry don't have any idea what Second Life is. They don't use it, so they don't know what people are getting out of it. So when they come to build a 'Second Life Killer', they build something that does not (as far as the average user of Second Life can see) have much of anything that competes.
Guy Bendov, co-founder of Journeys: "I'm not a Second Lifer. I have a life. But I felt like I was missing out on something big. Yes, I like the entertainment part. I like the connecting people. But I can't spend hours every evening to promote the character." (via VWN)
Bendov doesn't need to tell us that he's not a Second Lifer. He's wrong on so many fronts, that it's pretty obvious.
Digital Phocus comments (regarding Sony Home), "The product seems to take Second Life to the next level. By giving people their own apartment and "trophy room" to store major achievements, Sony cuts out a potential revenue stream but takes a step to getting the user more engaged by allowing them to customize their place."
Whew. Missed the point there too.
"[I]f we are willing to step out of the traditional OPAC and create a metaversal web site that allows our patrons to access all their Web 2.0 sites as well as their traditional web sites like e-mail. If we can make our destination fun and easy, we can compete with Second Life, Myspace, or Facebook." - Richard Gladys
A swing and a miss. Myspace and Facebook aren't anything like Second Life, and Second Life isn't anything like Web2.0.
"EA is also launching Sim Societies --- but can it compete with Second Life?"
Until you know what the users are getting out of Second Life - and manifestly, most of these people don't and aren't bothering to - most of the attempts just won't impact Second Life's demographic all that much. You can't improve on the formula if you have no idea what it is, right? Most industry watchers obviously don't - so basing your Second-Life-killing investment on what they say is probably not a good idea.
Spend a year in Second Life - and then think about it.