It works because they exported it. VAR=foo bar only sets it for the env passed to that exec or subshell, export VAR=foo && bar adds it to the current env then executes bar.

export VAR=foo && bar is dangerous because it stays set.

Ah, that's what I had done wrong, thank you! And agree I wouldn't want to just one-off export it and have it be set, better to not export it for one-liner one-offs for sure