I don't understand raspberry longevity
So I have a nice raspberry hedge on it's 3rd year. 10 rooted canes were donated to my by my wifes grandparents. I don't know the variety, but it produces a summer and fall crop and I prune it accordingly. However, I keep reading that the plants will bear for about 10-12 years. But why? What makes them stop bearing? I am removing 2nd year canes after they bear thier summer fruit, so why wouldn't the roots stay alive indefinately and just keep shooting up new canes year after year?
I currently have about 100 flourocanes left from last fall and there seems to be another hundred or so primocanes busting on up this spring. I don't even know if I will be in my current house for 10 years, but does it go from the date of transplant? If I dig some runners out and transplant them to a different area will it reset the 10 year count? I guess I just don't understand the mechanism for the plants to stop producing.