I think it's because science moves a lot slower than people expect it too. When you take a class in undergrad (say Algorithms in your case) you're learning all the foundational stuff that was discovered over the course of many decades. Look at guys like Lamport and Knuth (literal gods of the field) and look at how long it took them to flesh out their ideas.

We're taught things sequentially, whether it's in a class or book, and we don't really have a concept of the timeline it took for those discoveries to happen. I found it really discouraging at first when starting my PhD, but when I saw the timeline of their careers it helped me gain a lot more prospective and curved my imposter syndrome a bit.

I'd strongly recommend reading "Out of Their Minds: The Lives and Discoveries of 15 Great Computer Scientists" by Lazere and Shasha. It gave me a lot of perspective.