Because you are only hearing from those suffering the side effects. I was on Letrozole for 9 months with only the occasional hot flash. After surgery, chemo and radiation my oncologist put me on Anastrozole. My neuropathy started midway through chemo, but the joint pain started with Anastrozole and got so bad I was darn near crippled by it. I'm back on Letrozole and taking collagen supplements and have only arthritis related issues in my back. Everyone is different and everyone reacts to various drugs differently. Many people have little to no issues with these drugs. The quest is to find the right one for you.