Hydrofoils lost appeal because speed stopped being enough

Why did Pegasus-class hydrofoils and similar fast attack craft fall out of favor?

He says Pegasus tried to create a very fast attack craft, but hydrofoils became vulnerable once speed alone could not outrun missiles or compensate for limited flexibility.

Pegasus was an attempt to create a very rapid attack craft. Such vessels can become one-trick systems. If their speed advantage is neutralized or irrelevant, they have little else to fall back on. Missile-era warfare made it difficult for hydrofoils to justify themselves simply by going fast.