Actinoids exhibit a larger number of oxidation states than lanthanoids because the $5f$, $6d$ and $7s$ energy levels are of comparable energies (i.e., they have a lesser energy difference). This allows the electrons from all these subshells to participate in bonding and exhibit a wide range of oxidation states. In contrast, the energy difference between $4f$ and $5d$ orbitals in lanthanoids is relatively larger.