As far as I can tell, memorization is taking a set of information, and learning each piece of information one at a time. Memory palaces and spaced repetition are tools for “not forgetting” pieces of information, and they both can be essentially independent from the information itself. This is why they are generalizable strategies for “not forgetting”. I imagine they work best when put together, but I think the fundamentally interesting part of spaced repetition is that it’s not a mnemonic device itself, but instead an “effortless” retention system with pretty clear time costs.