Because like a lot of things, metric of "What does recruiting cost us?" is very easy number to quantify so companies will attempt to reduce it.
"What does bad recruiting cost us?" is very hard number to quantify because it's just sand that gets thrown into so many gears, but cost of that sand is across a ton of departments and so measuring for it is very difficult.
Huh? Hiring being broken has nothing to do with cost, it's a filtering problem. Even when there's no HR or bean counter in sight it's still hard. There's fundamentally limited signal you can extract from interviews, so there's very loose correlation to on-the-job performance. Saying it's a cost-cutting problem would just encourage more and longer interviews, which could actually work against you because high performers tend to have more options and will not jump through infinite hoops.