Why so few speakers with Passive Radiators?


What are your thoughts on Passive Radiators in speaker design?

I've had many different speakers (and like many here, have heard countless varieties outside my home), from ported, to sealed, to passive radiator, to transmission line.

In my experience by far the best bass has come from the Thiels I've owned - CS6, 3.7, 2.7 which use passive radiators.  The bass in these designs are punchy yet as tonally controlled, or more, than any other speaker design I've heard.  So I figure the choice of a passive radiator must be involved somehow, and it makes me wonder why more speaker designers don't use this method.  It seems to give some of both worlds: extended bass, no port noise, tonally correct.

And yet, it seems a relatively rare design choice for speaker manufacturers.

Always wondered how the passive could be in phase with the active speaker/s. Seems to me when the active speaker reaches some excursion out, that action would lower cabinet pressure that would suck the passives radiators in. Am I off base here? Perhaps someone could explain.
That being said, I'm  currently considering speakers with passive radiators.
I, also, have a pair os s400’s on order, and one of the main reasons is that ive enjoyed a pair of Vanatoo’s with passive radiators.  Very excited about the Buchardts!
I have never made a port noise complaint.
@rja2-  Refer to my post, dated 1-30, for the answer.
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