I've meanwhile read that they are networked very well, with fibre even, but only between each other when built in a park/farm. And often very remote, far from other inftastructure. The problem arises at the transfer/injection point from the utitility one level up. Not always, but sometimes, and in different ways. It can happen that there is no 3/4g at all there. It can happen that the other utility isn't networked(in a usable way). It can happen that the other utility doesn't want to network for whichever reasons, security, etc. And it can happen that you get 1Gb/s symmetrical there.

Apparently Enercon choose to offer its clients this solution as 'carefree package', to spare them the regulatory/bureaurocratic hassle of having to deal with this.