We use globular cluster kinematics data, primarily from the SLUGGS survey, to measure the dark matter fraction ($f_{\rm DM}$) and the average dark matter density ($\left$) within the inner 5 effective radii ($R_{\rm e}$) for 32 nearby ETGs with stellar mass log $(M_*/\rm M_⊙)$ ranging from $10.1$ to $11.8$. We compare our results with a simple galaxy model based on scaling relations as well as with cosmological hydrodynamical simulations where the dark matter profile has been modified through various physical processes. We find a high $f_{\rm DM}$ ($≥0.6$) within 5 $R_{\rm e}$ in most of our sample, which we interpret as a signature of a late mass assembly history that is largely devoid of gas-rich major mergers. However, a few of our ETGs have remarkably low $f_{\rm DM}$ ${∼}0.4$ and diffuse dark matter haloes that are not adequately described by Navarro--Frenk--White profiles. We find tentative evidence that lenticulars (S0s), unlike ellipticals, have mass distributions that are similar to spiral galaxies, with decreasing $f_{\rm DM}$ within 5 $R_{\rm e}$ as galaxy luminosity increases. However, we do not find any difference between the $\left$ of S0s and ellipticals in our sample, despite the differences in their stellar populations. We have also used $\left$ to infer the epoch of halo assembly. Our ETGs generally reside in haloes that formed at $z{∼}3$, with haloes associated with ${∼}L^*$ ETGs forming earlier ($z{∼}4$) while those of massive ETGs form later ($z{∼}2$) than average. By comparing the age of their central stars with the inferred epoch of halo formation, we are able to gain more insight into their mass assembly histories. Our results suggest a fundamental difference in the dominant late-phase mass assembly channel between lenticulars and elliptical galaxies. ; Comment: Submitted to MNRAS, 10 figures