why aren't ribbon tweeters more popular?

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.