Mazda itself had very little interest in pushing the Mazda 5. It's own internal sales projections are very small. And it has *NEVER* been marketed here. Have you ever seen a commercial for it? Mazda in general is a low marketing company having really only marketed the CX-5/9 recently.
The 5 has a couple things that hurt it's sales a bit.
1) It's still a Minivan. Look at vans in general, they've lost A LOT of ground to SUV's. People have a serious ego issue buying a car with sliding doors as if those doors have circumcised their livelyhood or something.
2) MPG & Performance + size compared to full size. On paper the Mazda 5 really didn't get any better (if not even worse!) milage than a full sized Odyessy. Factor in a somewhat doggy 4 cylinder and a major step down in size and a lot of people just didn't want to bother with them.
Now if Mazda would take the time to "Skyactiv" the little bastard and give you a vehicle that could carry six people, was fun to drive, had the turning radius of a tricycle, and when needed storage space that would humiliate most cute utes....AND give you 35-40MPG on the highway...that would be something special.
As a previous Mazda5 owner, they are very cool little cars. I loved mine.