While it's a big assumption that this is down to observational bias, at least there is some theoretical support for that statement. The further out a planet is,

While it's a big assumption that this is down to observational bias, at least there is some theoretical support for that statement. The further out a planet is, the less likely it becomes we can observe a transition event (which also becomes extremely rare). Now that only our system's configuration - as special or as common as it may be - is amenable to complex life is completely unrelated and unfounded.