Lawsuits like this list all possible parties that have money; so McDonald's, the local store, the local store owner, the distributor, any outside company any of the above companies use that could be linked to sanitation, all of them would be listed.
If the case goes to trial and the movant(victim) wins, then the jury/judge will assign blame as a percent of the total. McDonald's may have no liability despite being included, or they may have 10% meaning they need to pay that percent of whatever judgement was awarded.
Each named party can also independently try to settle to have their name removed from future proceedings.
If we did that then we'd just be the world's biggest illegal drug exporter and world's largest slavery, and world's most war hungry nation.
We need to be an arms exporter as well!