Link building became a volume game because volume was easy to measure and easy to sell. Send 10,000 emails, get 50 placements, report 50 links. The problem is that most of those 50 placements are on websites nobody reads, built specifically to host paid content, and recognized as such by both search algorithms and human readers.
The publications your audience actually reads — industry trade journals, major news outlets, respected niche blogs with real followings — don't accept paid insertions. They have editorial standards. Getting mentioned there requires a different approach entirely: you need something worth mentioning.
This isn't a new observation. What's changed is that the gap between low-quality volume links and genuine editorial coverage has widened considerably. The former has diminishing returns. The latter compounds.