I think it’s because the purpose of the Spline Effector is to move clones to a spline – make a mass of clones move to a font spline for logos for example. Offsets and such are just extras. That behavior (moving to the spline) overrides all when it’s used. If you clone the Spline Effected cloner and play with settings and alignment you will see that new clones do get generated but they all end up on the spline because that is what the Effector does.