Because:
All SciPost publications will obtain a unique DOI, enabling citations and metrics as per other journals.
The publishing landscape is evolving rapidly, and it is not clear that the best interests of science and scientists are being represented. SciPost aims to implement a grassroots solution by scientists, designed in the best interests of science itself, to the challenge of scientific publishing.
The initial rollout of SciPost offers a Physics portal.
Portals in other fields of science will be opened if the SciPost model proves to be successful.
Because:
SciPost operates non-commercially, encurring minimal costs. Contributors provide all the content and perform all editorial tasks as part of their normal institutional academic duties. Operations are kept running by a team of officers, themselves academically employed.
Support for operational costs is initially provided by the NWO in the Netherlands. Long-term operations will be financed by donations from national funding agencies, universities, foundations and individuals.
If you are a generous private funder, then yes, for the sole reason that this will motivate you to support our operations.
If you are a Contributor, there is no worry to be had. SciPost is from the outset established as a long-term operation and has no plans to shut down.
See the previous question/answer. In particular, authors should in no way worry that their SciPost publications could potentially disappear. This would require the dismantling not only of SciPost, but also of the arXiv (where the final version of the accepted SciPost papers (with unique DOI identifier) can be posted by the authors, and (since the papers are not behind a paywall) of the authors' own web pages. As long as the Web stands, SciPost stands.