Claude Code was released in February, it just had its 1 year birthday a few days ago.

OpenAI Codex CLI and Gemini CLI followed a few months afterwards

It took a little while for the right set of coding agent features to be developed and for the models to get good enough to use those features effectively.

I think this stuff went from interesting to useful around Sonnet 4, and from useful to "let it write most of my code" with the upgrades in November.