Gutter Brakets Snapped In Snow?

We are finding yet again this year that many homeowners are experiencing broken gutter brackets on their conservatory. If you have experienced snapped brackets and sagging gutters then we'd like to know what you believe the cause to have been. Does it look to have been caused by the shear weight of snow, too few brackets, or is the freezing temperatures more to blame? Brackets such as Wendland RS32790, K2 C8043 and Eurocell CRS-8207 can be bought through eBay to help those affected but we're interested in the root cause. Thanks in advance :-)