Comment by mike_hearn

Some of this is due to the adoption of React. GUI optimization techniques that used to be common are hard to pull off in the React paradigm. For instance, pre-rendering parts of the UI that are invisible doesn't mesh well with the React model in which the UI tree is actually being built or destroyed in response to user interactions and in which data gets loaded in response to that, etc. The "everything is functional" paradigm is popular for various legitimate reasons, although React isn't really functional. But what people often forget is that functional languages have a reputation for being slow...