Remember RayDream?  I liked it and became quite productive with it, even with all it's flaws and bugs.  Then, instead of fixing those flaws and bugs they came out with Carrara 1.  That was bad news for me because they changet the interface too much, never fixed many of the old bugs, and left out some neat things that Ray Dream used to have.  After that I started rendering in Bryce, realizing that I could create better renders with more ease.  The rest is history. 
Today we may have a perfect Carrara with state-of-the-art features, but changing ones 3D program is no trivial thing, especially when one has 7 years of skills and models invested in their old program.

"An Example is worth Ten Thousand Words"