What about part d?

(d) CREDIT TOWARD FLIGHT HOURS.—The Administrator may
allow specific academic training courses, beyond those required
under subsection (b)(2), to be credited toward the total flight hours
required under subsection (c). The Administrator may allow such
credit based on a determination by the Administrator that allowing
a pilot to take specific academic training courses will enhance
safety more than requiring the pilot to fully comply with the flight
hours requirement.

Congress required the ATP, and the FAA says how many hours it'll take. That's the cutout for the Restricted ATP at 750, 1000, and 1250 hours.