Why does reinstalling windows consume an activation?

I had to reinstall windows because my product activation key was for a different version of windows. I had to re-install capture one and it consumed an activation. Why? Are activations not per machine?

What is the point of deactivating old devices if you cant then activate a newer device. I have three devices but no activations left. I've already deactivated an older device but now I can't activate my new device and I CAN'T EVEN USE MY OLD DEVICE WTF!??

What's the point of a perpetual licence if you can't use it when you purchase a new device???