It's just a win/win situation.
One one side, business partners are happy to show their support to young startups and spread the news about their service by offering their software for free (for a limited period).
On the other side, startups can access great tools for free.
No sales pitch. No catch.
We chose to participate in this StartupPack project. We're just offering some services for free. We liked the idea and thought it could be useful for some fellow startups.