Gazebo uses exactly half of the cpu

Hi, I'm using gazebo 9 (the version that comes with ros melodic) in combination with ros. I'm simply loading a ground plane together with some hexapod models. I'm wondering why gazebo generates a cpu load of exactly half the maximum possible load. I'd expect it to use at least one core at full load but instead it uses all 4 (or 6 cores on another computer) at just half the maximum load. Perhaps someone could give me a hint if this is intended behaviour or if I misconfigurated something? Thanks in advance