Because 99% of the people on this board are concerned with getting the lowest cost product that meets their needs. It's more of a forum trend really, and is why most of us are here....we want to know what we're doing and spend the least amount possible to do it.
The IDMax is still a badas$ sub, but you're going to find people on here that are continually looking for different products to perform in their price range.
Now that we all know what an IDMax does, it fades away after awhile, similar to the W7 on this board from what I've seen in recent months.
But now that internet companies such as Fi are releasing new products to compete with these, the new products gain *popularity*. Doesn't make them better, but more popular indeed.
Personally, I find that subs meant to do similar things do similar things. There will never be an end-all product out there, just newer products as time goes on.
And like Camshaft says, people go by word of mouth. You're not going to see me running subs based solely on what forum mebers tell me. I have learned too much over the years and install is so important it's going to overrule equipment most of the time.