We investigate, both theoretically and experimentally, the mechanism behind the creation of a macroscopic magnetization in a gas of paramagnetic molecules with an optical centrifuge, reported in Phys. Rev. Lett. 118, 243201 (2017). Our analysis shows that the centrifuged superrotors and non-centrifuged molecules are polarized in opposite directions, while the net magnetic moment of the whole ensemble at the end of the interaction with the laser pulse remains close to zero. As the superrotors are more stable against re-orienting collisions, their spin polarization, which points along the centrifuge axis, decays slower than the oppositely oriented polarization of the non-centrifuged molecules. The latter lose their directional rotation much faster and with it the polarization of their electronic spin. We show numerically that owing to this difference in decay rates, a net magnetization in the direction of the centrifuge is generated. The proposed model is supported by experimental data.