Databases are interesting because they were the forefront of computing when it was invented, and they still are today. The computer science sorting algorithms and trees (and trie) go directly to how good (for all the different kinds of definitions of good) a database is.

MongoDB threw out a ton of history in order to invent a different wheel, and it's faster for interesting reasons, but it's also for a different era than single monolith computing (aka Oracle DB). That doesn't mean MongoDB is appropriate for all situations, but that a fundamental precept of computing has changed. Used to be, there was room for maybe five computers in the whole world. Today, my computer has multiple virtual computers inside of it and they are treated as cattle, not pets. The work being redone is because (sometimes) the work has been invalidated by newer experiments.

We're going to have to "redo" a lot work once dark matter is found as well.