Memoization implies caching specifically, which implies its own things, such as cache size and eviction methodology. Not something that's necessarily thought of when using the term "memory".

Memoization is close enough to "memorization" that you pretty much know what it is without having heard of it before and easily rememberable, while being specific enough to the actual concept as to be easily searchable and imply specific concerns of its own. That's a win-win in my book.