Jake got paid for Ultimate Sin i.e. songwriting royalties. For Bark, she gave him an ultimatum, sign over all your rights or we'll just have someone copy your guitar parts and send you on your way.
At that point Jake could have taken the crumbs or go back to nothing in LA. If you think about it he really had no choice, have a career or be known as the guy who couldn't cut it as Rhoads replacement because that is certainly how Sharon and Ozzy would have spun it. Jake also only made about $500 a week on tour. Hell Vivian Campbell got paid even less, he was making $100 dollars a week.
Further Jake wasn't a family friend, he just said in his most recent interview he hadn't spoke with Ozzy in 40 years until his final show.