Mainly because it cannot be trusted enough for this kind of application. 
It is not Open Hardware. The processor used is very closed, even the data-sheet is not accessible to the public. (It&#x27;s very problematic for a device like Own-Mailbox very sensitive regarding politic.) 
The Raspberry Pi is provided with non-free software and the hardware needs non-free driver to work. (Also problematic.)<p>Raspberry Pi is bigger and less energy efficient.<p>On top of that, we don&#x27;t use it for prices reasons, people have already tried to sell all-in-the-box devices based on Raspberry Pi and the end up being expensive.<p><a href="https:&#x2F;&#x2F;www.kickstarter.com&#x2F;projects&#x2F;1547898916&#x2F;own-mailbox-the-first-100-confidential-mailbox#project_faq_146547" rel="nofollow">https:&#x2F;&#x2F;www.kickstarter.com&#x2F;projects&#x2F;1547898916&#x2F;own-mailbox-...</a>