The reason is that there are certain configuration settings server-side which have to be set correctly for MfE Maemo to work.
Especially the "provisioning" feature is a hindrance for many. This feature is intended to provide higher security by making sure the mobile device adheres to certain standards. The ability to completely wipe a mobile device remotely is an example of a requirement for "full" provisioning.

This is currently not possible with Maemo, because as a Linux OS, it's open and customizable, and it would require too many changes on the OS side for MfE to be able to support provisioning.
This will change in the next iteration of Maemo ("Harmattan" / Maemo 6), because it will have a dedicated DRM mode which allows the developers to implement the needed features for provisioning.
On the other hand this will make Maemo less open, which has been the topic of a heated discussion, but it will (most likely, nothing is certain at this point) satisfy the requirements for provisioning.