I asked this question as well but by reading the whitepaper my understanding is the that they will just build it on top of Ethereum, it's a shame because there other better smart contracts platforms out there (neo, waves very soon for example...)
I don't know what they have planned for the future but Ethereum is the go-to platform for crowd sales so everyone does it. Many projects swap the tokens later on when they launch their own chain.
That is also my understanding and I would assume they would like to have their own blockchain which could be more suited to the platform as its grows.
If the current solution doesn't suit them at some point they can easily make their own and swap. But blockchain developing takes time and money and i think they are acting wise for starting as a token.