installing plugins in zartbitter.co.at

why is it not possible to install a wpmudev plugin like hummingbird directly out of the wordpress installation of zartbitter.co.at while it is possible to do so with agentur-dreirad.at! for agentur-dreirad.at it was a one-click install in the wordpress backend using wpmudev dashboard. for zartbitter.co.at you click on hummingbird install, it opens a new tab which directs me to wpmudev.org where i again click "install", and then nothing happens. the only possibility i have is to manually download it and install it like any other premium plugin via the wordpress upload plugin feature.... thanks