Freelancers' careers live or die based on where future work is coming from. Happy clients are good for repeat business. Happy clients refer other potential clients. Happy clients are good for portfolios or case studies. Smart freelancers are all about keeping their clients happy in the long term. It's just good business.
Of course there are people in the freelance world who are hopeless and will never build anything useful just like there are people in the employment world with the same problem. But it's much more career-endangering to be incompetent as a developer and/or as a communicator in the freelance world because freelance gigs can often be terminated relatively easily if the client isn't happy with the work.
Maybe this is different in the parts of the US where compensation for tech employees can be way higher than anywhere else but in most of the world freelancers tend to be relatively good at what they do and part of the attraction of going the freelance route is that it doesn't have the glass ceiling on compensation that being an employee often does so if you're good enough to justify higher fees then you can actually charge what you're worth.