Because there are people out there waiting to jump at any chance to sue you.
This firm is in Washington. They are willing to get on a plane and fly across country to represent the "consumer" (i.e., victim)...that ain't cheap, but they know they have a strong case.
Don't get me wrong. The people who got sick for eating at the place are going to be out a lot of money for missed work and medical expenses. Include pain and suffering into the equation and they should be compensated. However, if someone has to come across the country to "help" out the victims, then this isn't just about doing what's right. It's about money. BIG money.
It's sad really. The owner of the business is going to lose because one of his employee's (most likely) made an error. People got really sick, some one could've died. The only winner are the liars, er lawyers, who will take money from both parties.