Most 64 bit processors only use 48 or 52 bits for physical memory addressing. So you might have a 64 bit virtual address, but that gets crunched down to your real physical memory which might only need e.g. 36 bits for 64GB RAM.
You rarely actually use 64 bit integers. So much of the processing is on strings which use 8 or 16 bits.
Furthermore, your Intel x64 processor still contains the features first introduced with the first IBM PC using the 8088 which in turn was conceptually compatible with the 8008 and 8080. When you try to understand a modern Intel or AMD CPU, you need to be aware of the legacy of 40+ years of backward compatibility. Once you understand the historical decisions, SSE, AVX architectures start making more sense.
You rarely actually use 64 bit integers. So much of the processing is on strings which use 8 or 16 bits.
Furthermore, your Intel x64 processor still contains the features first introduced with the first IBM PC using the 8088 which in turn was conceptually compatible with the 8008 and 8080. When you try to understand a modern Intel or AMD CPU, you need to be aware of the legacy of 40+ years of backward compatibility. Once you understand the historical decisions, SSE, AVX architectures start making more sense.