I think one problem is that these days you use so many frameworks and libraries that is hard to get a good mental model of how software performs and where bottlenecks are.

Another problem is that performance often given lower priority in enterprisey software development. For example, i'm currently working on a project where two componenens share data through a message bus. The architects decided that all messages on this bus have to use json with a bunch of headers. For my project, it could literally be 50x faster with very little effort if we could use a more efficient format, but it is not allowed.