Professional service companies are vulnerable to lawsuits claiming issues with the rendering of said services. Every organization makes mistakes naturally, but these mistakes have legal grounds for claimants to seek compensation for real or interpreted harm due to issues like underperformance and failure to perform services as expected.
PSFs are also vulnerable because they handle large amounts of sensitive data, including personally identifiable information. Failure to properly manage this data can result in data leaks and data breaches by hackers. If a client is harmed because your data was not secure enough, you can be sued for any damages they incur as a result.