I believe it has more to do with what the carrier is FAA accepted to train for.

At my previous airline (circa 2000), the circle was trained/checked in the sim, with NO restriction placed on the type rating. And that was under an AQP program with 100% of the training done in the sim, no 15% ride. Later, the company (like many others) was no longer authorized to execute a circle unless it's VFR mins, which pretty much seems to be the standard now. But when we did train/qualify in the sim, it was done right at the circling mins for the approach used, NOT 1000' and 3 that's later required to execute a circle. And it's NOT like the FAA wanted all the type ratings back so they could put the circling restriction on them.

I've had this conversation multiple times whilst on my long commutes on mainline carriers. If the guys got their types on the aircraft in the 90's, etc they don't have the restriction. Guys that upgraded or transitioned at later dates do have the restriction.