There are at least two answers to that question:

1. Knowing things lets you know more things faster and they stick: associative memories are very durable because they are mostly groups of references to existing objects in memory. Much less novel information that needs to be encoded. Repetition and memorization matters.

2. Look up latency: Same problem as computer cache misses and L1 vs RAM lookup times. You will take 100x longer to achieve the same result by looking up reference material all the time. Also important questions typically have answers from many different problem domains (social, scientific, philosophical, ethical) and its important to have a lot of knowledge memorized to see a solution to a novel problem holistically.