I am one of the ZoL developers. I assume that you are referring to the PPA and EL repositories. The ZoL PPA and EL repository maintainers use DKMS there because

I am one of the ZoL developers. I assume that you are referring to the PPA and EL repositories. The ZoL PPA and EL repository maintainers use DKMS there because there is no way that a third party can ship kernel modules at the same time a distribution ships a new kernel. That means that there would always be a window of time where the new kernel is available and the modules are not, which breaks things. Furthermore, keeping up with new kernels from upstream to publish binary modules is a burden that DKMS eliminates. if it were not for those things, the upstream project repositories would have had binary modules available years ago. Since Canonical is in the position to avoid the race, they are able to ship the binary modules that the upstream project could not.