Why navies did not build a double-razée frigate directly

What design logic would produce a frigate equivalent to a double-razéed first-rate?

None that is economical: a razée works as a conversion, while a strong purpose-built frigate should follow a dedicated frigate design.

Razées gain their unusual power by reusing the structure and rig of a ship already built for the line of battle. A purpose-built frigate follows a different design logic, as demonstrated by the large American frigates. Constructing a first-rate and immediately removing decks would consume first-rate money without obtaining a first-rate's role. Both naval administrators and Parliament would object loudly to such an intentionally wasteful path.