why aren't ribbon tweeters more popular?

What is the downside to ribbon tweeters? I haven't had any in a long time (Phase Linear P580's, stolen, still miss them.) Ribbons offer great extension and speed; other than expense, what objectionable qualities limit their use?
A lot of speakers have ribbon tweeters these days, it not really uncommon at all. Like any other technology, some people like them and some don't.
Downsides—delicate, easily overdriven, higher distortion, beaming dispersion pattern. Ribbon and quasi-ribbon also exhibit edge resonances and a rising frequency response, some more than others, making them difficult to work with and listen to. However, these traits are attractive to aging boomer ears with hearing loss.
Ojgalli Only thing I agree with is delicate but they can be easily repaired unlike other transducers. Ribbons can image wonderfully can produce accurate sound and measure well. Sure are not difficult to work with I do so daily. But some have such biases they can not except the fact that ribbons are just like any other transducer used in audio and if done right a hi quality loudspeaker can be designed with ribbons or most any type of transducer. Happy listening.
Evolution Acoustics and Aerial Acoustics use these on their top flagship speakers.
Nuff said!
Old Apogee Duettas or Divas kill almost anything made today. When rebuilt by Rich Murry at Truesoundworks they are amazing and among the best I have enjoyed. I have listened extensively at friend's system to some of the most expensive finest speakers made today or have tried in these speakers in my own system and keep going back to Apogees. Apogees in stock and or with moded crossovers they kill just about everything. Apogees when re-ribboned they kill everything period. With planar and ribbon speakers you are at a performance with dynamics speakers in most cases you are in a recording studio. Nothing wrong with either venue but that is the difference in sound.
Hi JohnK,

Have you heard/used a ribbon whose sound gets close to the t500mkII?
I actually think the main reason is that they are difficult to integrate with dynamic drivers.

Tonian does it extremely well, somehow.

They also don't have the dynamic snap of a cone tweeter.
The amk2 Is one of the better hi frequency transducers available but RAAL ribbons are wonderful in there own right and 1 can design fine sounding loudspeaker with either transducer. Where design would be best if a amk2 is used a ribbon wouldn't be the best choice, same where a RAAL would work best that design wouldn't be so good for amk2. Hope this makes some sense ;) They are not inter changeable.
I think the down sides are dispersion patterns (in some designs) and difficulty integrating them. However when implemented well they I find them excellent.
Agree with Ojgalli statement of "Downsides — delicate, easily overdriven, higher distortion, beaming dispersion pattern."

These are well known and accepted drawbacks to ribbons and it answers the OP's question of why they aren't used as widely as other types of tweeter.
Shadorne modern ribbons are not easily over driven. And they do not have distortions thats are musically significant. Much of the - about ribbons of late comes from Zaph audios test link. To some cheap ribbon dome comparison. But if they looked more they would see Zaph is offering most loudspeakers with ribbons. And RAAL has eliminated the dispersion issue which isn't hard at all for a loudspeaker designer to work with. And can be an advantage. I have never had a ribbon loudspeaker KCS manufactured returned due to ribbon damage. And if it did would be a easy repair. I see so many loudspeakers using ribbons today I thought about listing but just to darn many so the whole premise that ribbons are not popular is just not true. Sure more domes about but then they are far more affordable and thats why so popular.
Ribbons can sound clear and transparent if you are there in the sweet spot. However, stand up above the ribbon location and your top end disappears quite a lot. They also don't seem to have the naturalness of a silk dome tweeter and, although fast sounding by themselves, they can sound a bit disconnected from the cone mid/bass driver.

However, silk domes vs metal domes also have their own inherent problems. There is no perfect picnic.
What about the BG PDR3 and PDR8 tweeters? There low in distortion and have a wide dispersion.