Because they don't cause as much damange. They still cause damage arbitrarily, causing atrocious injury to people, but whatever.
Instant Runoff Voting is non monotonic. In rare circumstances, placing a candidate higher in your list will actually cause them to lose. Instant Runoff Voting is subject to voter manipluation, but only as much so as the current system, so I can't really complain about that.
Condorcet voting, on the other hand, is monotonic, and almost insucceptible to voter manipulation. The trade-off there is that sometimes you don't know who wins. :)
Let me be more clear. In condorcet voting, which requires people to use the exact same ballot as Instant Runoff and just counts the votes differently, you can end up with a circle of "winners" such that candidate A defeated candidate B, candidate B defeated candidate C, and candidate C defeated candidate A.
You'd hardly believe it was possible, but it is. It accurately represents a real ambiguity in the opinions of the voters. The fact that these sorts of ambiguities CAN exist is the very reason that most other voting systems are considered ineffective. They don't reflect things like this.
In an ideal world, you would keep having elections until the community lost its ambiguity, and picked a condorcet winner. In the real world, you have to pick a method to solve these ambiguities, and each of the methods for solving them have tradeoffs.
There is also a question as to whether or not having condorcet winners elected is actually a good thing. On average, people will tend toward the centre. That's why it's called the centre. Which is more effective, a parliament comprised of 100 representatives aligned generally with the centre, or a parliament comprised of 100 representatives, representing the actual proportional distribution of the individuals they represent?
I don't know the answer to that question. But if we decide to change voting methods in a single-winner contest, I'm voting for condorcet over Instant Runoff any day. (See how my opinion, in real life, is a ranking? Neat, hey?)
And that's all without opening the can of proportaional representation worms.
Into Canadian Politics?