Why doesn't my processor have built-in BigInt support?

Question

As far as I understood it, BigInts are usually implemented in most programming languages as arrays containing digits, where, eg.: when adding two of them, each digit is added on

Answer 1

As I think, the main idea behind not including the bigint support in modern processors is the desire to reduce ISA and leave as few instructions as possible, that are fetched, decoded and executed at full throttle. By the way, in x86 family processors there is a set of instructions that make writing big int library a single-day's matter. Another reason, I think, is price. It's much more efficient to save some space on the wafer dropping the redundant operations, that can be easily implemented on the higher level.