2. Getting a client and working on a paid project gives me plenty of direction as to what to build in my spare time.
3. What?
4. You're only getting money if they think your idea is best. One person/group wins, not everyone. You could have been doing something with guaranteed pay, not spec work.
5. Sure, you get new ideas on the table, but that doesn't mean they're good ideas. Not to mention you're giving away free ideas.
6. You're not really getting feedback from the community. You're getting it from the corporate sponsor.
7. No. They'll simply award the winner(s) $10k for IP and off they go. A win for the company.
2. Participating in hackathons is an easy, passive way to participate. It also doesn't leave the opportunity to fail as easily. If you mess up or get bored of the hackathon, you just stop. You're not screwing over a client-base. If this is your first project like this, you can even use it as a litmus test of whether you want to keep doing this type of thing, or not.
3. A common goal. There's an idea that maybe you hadn't thought about before; and now you, and your friends, can focus on this goal. Also, you, your friends, and several other people who found an interest, can all work on developing a new thing. It'll probably be more innovators than a normal team that would be designing the new machine.
4. True, but it's still nice incentive. TopCoder contests have prizes for the best contestants, too; and some of those are especially sponsored in much the same way.
5. You never know a good idea until you see it executed; and... so? Some people are freely willing to do that.
6. You, the company, are getting feedback from the community by some of the people in the community making a version of the product that handles some of their problems with the current models
7. Maybe, maybe not. I'm not Coca Cola. They /could/ use it for scouting, even if they don't.
That new ideas, informed feedback, and talent are valuable assets is obvious, so why should you hand them over for (virtually) free? That only devalues the value of the skills, training, and experience required to arrive at those insights.
Is there some cross-team protection or NDA taking place for all the contestants?