Some of the unevenness is for occasionally non-obvious, but valid reasons. It's done in RoHS, too, for instance: lead is banned out of solder, but still allowed for some equipment, such as radiation shields for imaging machines.

The reason being that lead-free solder can still be used effectively. Lead-free radiation shields -- not so much.

The aim is to reduce the usage of hazardous substances to those cases where there's just no way around them, in the hope that it will make things like waste management easier.

Edit: CE marking requirements are also reasonably easy to work out. I know several one-man businesses that solved that problem without that much hassle, so -- anecdotally -- the minimum size imposed on a business is one :).