The debtor can't "vanish", they are either an individual or an entity with registered individuals attached to it. Obviously, their structure matters a little bit along with where they are incorporated. But if they are incorporated in California, their debt is 95% recoverable if they want to continue doing business in any way. As an individual you can go after garnishment and other relief. As an entity, it's similar but to their company/corporate holdings.

If they try to dissolve and create another business that operates in the same sphere/as a successor or with the same management team; the debt doesn't disappear, you just prosecute the new entity. With an added cherry of potential criminal prosecution, if they're particularly egregious about it.

People can 100% get around paying, that happens. But the judgement will remain on their record. This will make reincorporation difficult as well as just acting as a warning to future partners that do basic due diligence.

No one's saying it's easy to get the money back, but rolling over probably is the least desirable outcome (and probably why they've acted this way with so many people).

As to your collection firms, I can't speak to it. Maybe your situation is more complicated (e.g. registered entity out of state, unclear contract terms, etc) or they just don't want to go through with the hassle of doing more than they were hired to do (send nag letters and hope for easy turnover).

In the future, you can use it as a learning experience. Keep your deliverables under the small claims limit, do metered payouts, etc.