Getting to work directly for/with a CEO or main decision maker, for free or not, is probably at least as hard as getting a real job. Most people don't have a stash of work lying around that a person with unknown credentials and no context can just pick up and execute. Bringing a person up to speed to do real work takes real effort which is wasted if the person doesn't work out - so if you need an extra person on the team, you'd rather spend some time making sure you're hiring the right person, and then we're back to square one.
Then there's the issue of unpaid labour to do indispensable work to begin with: Unless in a well-defined intern position - that is, a person that isn't actually expected to achieve much besides some hands-on learning - it's culturally poisonous to have unpaid labour around. As a boss, you're telling your employees (the ones that get paid to do indispensable work) that there are people who can and will do their jobs for free. If that's not the case, then what you're doing isn't actually indispensable, and won't give you much leverage.
I'm sure the method worked well for you, but I'm also quite sure that there were specific circumstances in your case that facilitated that success, such that it doesn't translate directly to general advice. I'd even venture a guess that those circumstances, applied slightly differently, could have resulted in a regular job.