How long did you own the Mirage bipolars you are referring to?
I've owned a pair of Mirage M5si's for over 20 years and they are amazing speakers. The imaging is not mini-monitor great but it is very good, the soundstage is huge, and I've not noticed them being hard to position or set up. All of the negatives you hear are generally from people who have never owned them. There have been plenty of bad examples of bipolar speakers over the years but the Mirage M series have been among, if not "the," best. Just have a look at some pro reviews.
Why aren't they popular? Because you can get more bang for the buck without the added design complexity and expense of the rear facing drivers. Like most high end product design it's a niche. Some people like the sound and some don't. I'm a professional musician, 25 years, and to me they sound more like what I hear live. Traditional directional speakers sound like what I hear in the control room, not the tracking room.