CPU Caches are powers of two because retrieval involves a logarithmic number of gates have to fire in a clock cycle. There is a saddle point where more cache starts to make the instructions per second start to go back down again, and that number will be a power of two.

That has next to nothing to do with how much of your 128 GB of RAM should be dedicated to any one data structure, because working memory for a task is the sum of a bunch of different data structures that have to fit into both the caches and main memory, which used to be powers of two but now main memory is often 2^n x 3.

And as someone else pointed out, the optimal growth factor for resizable data structures is not 2, but the golden ratio, 1.61. But most implementations use 1.5 aka 3/2.