Is the idea that password hashes should be slow relatively new?
It's just that security wasn't as important (limited web attack surface) or generally understood back in the day (so people were even less likely to ask "is this hash suitable for passwords rather than checksums/indexing/etc?" than they are today), or the slow ones from then were fine -then-, but advances in hardware, the availability of the cloud/GPUs (so massive parallelization without a cost of infrastructure only a nation state could afford), etc, means they're easily compromised today.
The idea that password hashes should be slow is indeed relatively new. Also it's contemporary to the idea that algorithms should have salts builtin, so those features usually go together.