If I am not mistaken sometimes this is due to yield rates in chip manufacturing. Iirc there were 3 core pentiums at some point that were basically faulty 4 core chips where one core did not pass QC.
This is extremely common on CPUs and GPUs. gx104 from Nvidia was famously identical to gx100 with cache, cores fused out, probably because they were defective. It's a good way to increase yield for monolithic dies.
