Software engineers, like everybody else, are absolutely liable for errors. However, their work is invariably licensed using a contract that disclaims liability.
Regulated professionals, by contrast, are often limited by law from disclaiming liability or otherwise shielding themselves from liability (e.g. by using a corporation). This is especially true for highly regarded professions like lawyers and doctors. Professionals and licensed workers more generally are also usually required to be bonded or carry insurance so that they're not judgment proof.[1]
[1] The reason you would rarely see a software engineer employee (or any employee) sued for negligence is that it would be a waste of money--they wouldn't be able to to pay a judgment. You sue the employer not because the employee isn't liable, but because 1) it's easier to prove a case against an employer and 2) the employer is the only one able to afford a judgment. For example, if a UPS truck driver runs you over, you always sue UPS. You may or not may not sue the truck driver, but unless the truck driver is secretly rich it's UPS you're expecting to pay out.
Regulated professionals, by contrast, are often limited by law from disclaiming liability or otherwise shielding themselves from liability (e.g. by using a corporation). This is especially true for highly regarded professions like lawyers and doctors. Professionals and licensed workers more generally are also usually required to be bonded or carry insurance so that they're not judgment proof.[1]
[1] The reason you would rarely see a software engineer employee (or any employee) sued for negligence is that it would be a waste of money--they wouldn't be able to to pay a judgment. You sue the employer not because the employee isn't liable, but because 1) it's easier to prove a case against an employer and 2) the employer is the only one able to afford a judgment. For example, if a UPS truck driver runs you over, you always sue UPS. You may or not may not sue the truck driver, but unless the truck driver is secretly rich it's UPS you're expecting to pay out.