I found that while printing my bearings using Z-ABS and Z-HIPS that Z-HIPS bearings slide more easily while offering a tight grip on the rods it slides on, Is it smoother as a material compared to ABS or is this finding due to another reason?
Might be the lower shrink of Z-HIPS, the hole for the bearing should come out slightly larger with it. As long as the preload is sufficient for the load, the bearing should feel just as stiff with the lower preload (as long as the load doesn't exceed the preload) because both materials have similar mechanical properties in terms of stiffness and strength. You could try adjusting the size of the abs part slightly and see. Also, it's possible their coef of friction differs significantly... but both ABS and HIPS have a wide range of formulations, so it might be hard to look up though. So if they still feel different after tweaking size, likely this.
If the bearings are riding on stainless steel rods (not regular steel), you might try Z-PCABS as the wear rates have a better chance to be reasonable.