Engineering (G): The character is skilled in planning, designing, and constructing castles, towers, roads, and so forth. Any character with this skill can evaluate constructions the party is passing through to assess what shape they are in, when and by whom they were built, etc., with a proficiency throw of 11+. Each time this proficiency is taken, the character can supervise 25,000gp worth of permanent construction. A character who has taken this proficiency four times could work as an engineer specialist, as described in the Hiring Specialists section.
I’m a little confused about why a character with Engineering needs to take the Prof 4 times in order to work as a specialist.
If the character can supervise 25,000gp worth of construction with 1 prof, why wouldn’t they be able to act as a specialist overseeing construction up to that cost?
Thanks.