Could it be that your cutting mat is worn out?
I have noticed the same thing! i clean them and turn them over and usually only get one more project out of them.
My blades last forever. I only change them when I think they are going to die of old age. I think the angle that you hold the blade does make a difference and I try to cut at different spot on my mat. Once I made a Buggy Barn pattern, and had to cut 18 layers. Changed the blade that time, but it cut just fine. I use Olfa and an Olfa mat. Also try not to hit the edge of your ruler. I think that dulls the blades.
I have noticed my blades don't seem to last very long. I did get a new mat.. it helped some but .. I still don't get the life I used to out of my blades.
I too have this safe problem. The first ones I had lasted for over a year, I changed them out and didn't even make it through one project! I bought the Ginghers ones and the Harbor freight ones, could not tell a difference, both lasted less than one project! So frustrating!
I just bought a new cutting mat, beba's and I just love it. My cutters have never worked so well. My old mats were well used and soaking did not restore them. So maybe your problems are not the blades.