Yes, this is due to new physics in X-Plane 12 - they are representing real world effects, but are probably a bit too strong in the case of our 737.
Austin models the downwash of the wings making the air go "down" behind the wings - and if the horizontal stabilizer is in this downwash, it gets more effect (pushes tail down).
So if the plane lifts the nose, the tail moves close to the ground into an area where the air can not "flow down" anymore (because the ground is in the way). It looses effectiveness and the pilot has to "pull more" to make the nose keep going up.
Once the plane is out of the ground effect climbing, this effect gets re-established and you can "relax" the pull a bit.
The real 737 has the same effect: You initiate rotation fairly easily, then the plane "stops" rotating when you reach about 10 degrees and you have to pull MORE to keep the nose going up (recommended is 3 deg per second rotation rate). Once the plane is lifted off and climbs out, you can relax this extra pull. Its almost as if there was a "resistance" to the nose moving up around 10 degrees pitch.
It works the same on landing, the closer you get to the ground, the more you have to "pull" to keep your nose from dropping. This is more pronounced now in XP12 and one has to adjust the technique: When passing 50 feet, make sure to keep nose up at the same pitch! When passing 30 feet, pull nose up by 3 degrees and HOLD IT THERE. At 20 feet, pull power back to idle.