Why do Harbeth speakers have such a cult following

For me Harbeth speakers walk that fine line between being overly detailed and being boring.  They seem to capture every nuance of each instrument and vocals and do a great job of separating them without distortion or glare.  They are also very dynamic with, with notes coming from seemingly nowhere instantaneously.  I wish I could put it into words better.

I've been listening to Steve Miller's Welcome to the Vault the last couple of mornings on Qobuz on my little computer system with the P3ESR SEs, which I picked up for $1400.  The cymbals, the drums, horns, vocals, guitars... everything has so much detail and with a little help from a SVS SB-12 NSD subwoofer, the bass blends perfectly.  When listening to some of the live cuts, I feel like I'm sitting in the club with Steve and the band.  All of this in a small room with wood paneling, no room treatment, the speakers stuck in corners, and me sitting at my computer, about 2 feet in front of where the speakers are.  In a good room with proper set up... 

I've heard "better" speakers, but I can't think of any that I enjoyed listening to more (including my Super HL5 Plus).

All the Harbeth fans who have posted here are correct.
Harbeths are all that.

However, and this is a big one for me - they do not rock and do not have sufficient PRAT for Rock or Pop.

@mapman 
every harbeth model can convey a sense of vocal clarity and realism because that it the mission of their BBC heritage- to reproduce voices in a clear, uncolored natural presentation.  
Of the several times listening to the 40.1 and 40.2 I felt they were extremely natural sounding even with brighter recordings.  The depth of bass from the larger woofers softens the sound somewhat.  
The brightest , clearest sound to me comes from the SHL5+ of which I own.  I just love the sound of these speakers.  
I have owned the C7ES3 as well and they also have fantastic vocal transparency with a touch more richness from cabinet warmth.
The 30.1 / 2 and the P3ESR to me sound more like the 40.2, clear yet with a warmth and treble roll off that softens the sound just a bit too much for me and my system.  
However all Harbeths can respond quite well to system changes that put the sound in a direction more to your liking including room position,  interconnect cables, speaker cables, tube changes (if you have them) etc.    
To the notion that they are not energetic enough for rock and pop I completely disagree.  System synergy in source and amplification can make them very competitive with speakers that have dynamics as their strength.  

Interesting discussion. I have a couple of comments:

1) I don’t think Harbeth speakers are popular due to effective marketing or just because Stereophile highly rated them. Anyone who has ever relied on someone else’s ear to guide them most likely had been disappointed.
2) they can’t rock. That is false. I listen to a lot of good rock, Yes, Steely Dan, Gregg Allman, Mott the Hoople and many others. They sound realistic and great. They may not add artifacts like ear bleeding treble or artificial bass, but they are extremely realistic and faithful to the recording.
3) There is no “best” speaker in and of itself. You have to take so many their things (room, personal tastes, equipment, budget..) into account

so I think we are trying to answer an unanswerable question...like how many feet is yellow.

i can say that in my room, with my tastes, a Rega vinyl front end, with Exposure electronics make my Harbeth 30.1s sing 

two last things. I have heard it said that Harbeth speakers are what people choose when they are tied to listening to speakers. That is me. And secondly, with the Rega/Exposure/Harbeth set up. I spend a whole lot more time listening to music, and not my system

Good luck on the search. That is half if the fun.