Why naval hydrofoils remained a niche technology

Which navy produced the best hydrofoils during and after the Cold War?

American hydrofoils are singled out as interesting examples, but no definitive winner is selected and their practical usefulness is judged limited.

American hydrofoils are singled out as interesting examples that appeared for a relatively short time. The broader assessment is that navies found the idea appealing without finding it especially practical or useful. No specific design is selected as the best.