First of all, you get invited for a reason. That is:

- Current player needs people to sign their FC papers so they can create it.
- FC needs at least 4 people so they can buy a house

or

- They just want random people inside for fun and to flex how big their FC chest is while you will never get anything. Honestly just make your own FC and benefit from it. There's no point to join some other FC.

Sometimes it is good to stay in a dead FC because you can take ownership and then you run it for yourself.