Because the only incentive there was, was to buy Artemine. Most Artemine investors have already bought their genesis addresses, so mne has no use anymore. All the devs need to do is write up a clear whitepaper/roadmap for Minereum and prices wil quadruple within a week. They need at least 2 more goals for each project; a lottery and global app for Minereum simply won't be enough, and ICO factory and genesis address marketplace for ART won't be enough, they need collabs with established coins/brands.
Personally, i think they should start by having ART and MNE run completely side by side, like we should be able to invest in the Minereum lottery with ART, we should be able to pay our monthly fees for the world app with ART, we should be able to pay for ICO launching with Minereum, we should be able to buy a genesis address with Minereum, ...