The trouble with shrdlu and all the other early "natural language" parsers is that they weren't really parsing natural language. They parsed a formal language with syntax designed to look kinda like English.

At the time it was believed (by Chomsky, etc) that natural language could be described in formal terms and parsed by fixed rules. But after several decades of failed parsers (and the success of statistical methods like LLMs), it is clear that formal and natural are fundamentally different types of languages.