It's because claude code will test its work and adjust the code accordingly. The old way, with the way Cursor used to be or the way I used to copy and paste code from ChatGPT doesn't work because to iterate in towards a working solution requires too much human effort, making the whole thing pointless.

Cursor & its various clones (Cline, Roo Cline/Code) did that too, before Claude Code was even released.