This one is simple. The CPUs stop selling after not-too-much time (around a year or so) and i just want to mention that most CPUs are discontinued two or three years after release, and that sales don’t die out as quickly as visualized.

It's a balancing feature, I don't want people to be able to live off just one CPU forever. I will be making adjustments to lower the daily sales and increase the sell time once it's possible to have multiple CPUs selling at once.