What ended up happening is some recipe developers would try and actually reduce the amount of time their recipe took, and others would just "shorten" prep (or even cook) time down, to try and get the most clicks. I know Kenji talks about it in one of his POV videos, but I couldn't find it in a cursory search.
Since there isn't really a reliable way to know how long recipes would take for _you_ across different sites, it's almost not a useful metric, but it is what's been optimized for.