They get to keep as much as 80% with the Social Consensus and they get a built-in community of users, developers, boosters, investors, supporters. That takes time and great expense to build. When these high tech companies spend $12 Billion on some startup, it's not just the technology they want; it's the user base. The value of the BitShares community is incalculable; it will soon be worth billions.
For a business owner, entering into a financial relationship with a 20% minority investor is standard practice. When that minority investor comes with enough viral power to launch your 80% of the project into one of the top crypto-businesses in the world, then it's pretty dumb to ignore that. That 80% is worth magnitudes more than a non-compliant business. For developers/owners who want to do it all themselves, an extra 20% will be worth far, far less. 20% of nothing is still nothing. And that's not counting the negative wave they'll have to overcome when this community blackballs them -- the extra expense and effort of counteracting that bad PR will be a dead weight forever.
When you really think about it, the Social Consensus is a no-brainer.