The immune system in the gut has a complicated roll: it doesn’t just find bacteria and yell “bacteria! We have an infection!” Thus it needs to be able to tell t

The immune system in the gut has a complicated roll: it doesn’t just find bacteria and yell “bacteria! We have an infection!” Thus it needs to be able to tell the good bacteria from the bad. How does it? It constantly surveils the gut flora and builds a tolerance to the regular players. When something changes then it has the opportunity figure out if this is worrisome. Thus you can see how the appendix could be part of this surveillance mechanism. Of course we still don’t fully understand this entire system so this is all hypotheses at best.