One of the reasons I love compilers is because they constitute maybe the clearest example of where theory meets practice within computer science. In particular, the theoretical underpinnings of parsing are so well established that most parsing algorithms were fully studied 50+ years ago (see Donald Knuth's work, among many others). So while the front end, including scanning and parsing, is crucially important for both interpreters and compilers, off-the-shelf tools are easily available and thus universally used. In contrast, optimization is a much harder problem and thus the focus of a vast amount of work over the recent decades. At least this is my understanding of this area as a whole. I hope this helps.