Because wireless-n spec was not designed to be used for long range. Period. Wireless n is a excellent I totally aggree. You even get the max 240mbps. Try achieving that at longer range (lets say > 15KMs) and you will know. I was trying to educate people not to fall for some of the advertised gimmicks you see.
You even get 108Mbps with WaveSprint Turbo which will do 90Mbps of video so, using n spec doesnt serve any purpose here. We use n spec radios as well for smaller systems requiring higher capacities but that does not mean we want to do away with 40KMs WaveMax units which work on older technologies but will do the job. Also all Wavesight equipment comes with free monitoring software locally and remotely (separate device - not free) over GSM. It has link diagnostic test as well.
I tend to test a lot of gear and some of the expensive n spec radios out there really do the job quite very well, although I cannot comment on the max ranges they are capable of. If you do come accross any, kindly let us know.