Because it cools better. Zalman really hasn't updated their coolers since the pentium 4 era and because of this they are over priced and dont cool as well as newer models.
More heatpipes means more heat can be carried away from the CPU faster....more fins means there's more surface area to dissipate heat away from the heatsink...a larger 120mm fan means more air moving over the heatsink
The zalmans are overpriced but still perfectly fine coolers plus with space limitations they can be useful I have a 7500 I think it is not sure (cba too look it up) and it worked well and was 1mm short of the top of my htpc case