Could have simply been so familiar with the area that they were mentally running on autopilot without realizing that things were happening differently this time.
A speed limit of 15 mph over a No.12 turnout with 22 foot straight points is very conservative. With long curved points as described in the report, that was extremely conservative. 20 mph would be more usual on this size turnout with straight points. 25 mph would be beyond the norm with straight points, but would be OK with the long curved switch points. A speed of 30 mph through this turnout with the long curved point would be a step to far in my mind, not because of safety it woudl be well within the limit of safety, but because of the wear rate on the rail and the ride quality jerk rate. To give some scale to this, 15 mph speeds through No. 8 turnouts are the usual unless the overall track condition is poor. The old "rule of thumb" was that the speed through a turnout could be up to twice the frog number, in other words, 24 mph through a No. 12.