The 2.5 is better suited to Mazda 3 and Mazda 6
There could be other issues too but unless Mazda says something then probably extra weight is the issue.
Interesting observation.
I'm a little late to the party, but my following .02C worth is not scientifically or technically based.
It is based purely on my butt dyno:
When shopping for a new ride last fall, I/we were already leaning towards a sedan vs. CUV.
To be fair though, I test drove the CX-5 as well as the 6, back to back.
The difference was noticeable.
The CX-5 felt heavier (which it is), slower (which it probably is), less athletic and spirited.
The 6 is also not as tall, so it's centre of gravity is lower, which makes a big difference turning corners.
The 4 banger in the 6 is more than adequate, but the CX-5 somehow felt underwhelming after driving the 6.
I really wanted to love the CX-5, and would still choose it over the competition if I was buying a midsize CUV, but compared to the lighter 6, it left me wanting for more.
Like others have said, if Mazda could somehow be convinced to drop the turbo in the CX-5, it would put the competition to shame.