Apparently due to silicon degradation.
It's funny, because I have never experienced that, and I've always OCed and over volted my CPU's. My current CPU is a 7 year old Ryzen R5 1600, that I have been running with both OC and higher voltage too. Every CPU I've had for 40 years now, has been replaced because they became obsolete. I've worked as an IT consultant for 10+ years in the 90's and 00's, and NEVER experienced silicon degradation. All sort of other problems, like faulty soldering when led became illegal, and capacitors when fake poor quality Chinese capacitors found their way into production. There is no way silicon degradation should be an issue within a short time span of a couple of years.
Anyways as it looks now it doesn't seem like a good idea to buy Intel.