The person who pays for everyone may still need help with the work of arranging the occasion.

Paying and organising are two different contributions, and they get confused because only one of them has a figure attached. Booking, chasing, remembering who cannot eat what, arriving early, staying late: none of that is visible on the bill, and the person who covered the cost may be doing all of it as well.

At the next gathering, ask the host what still needs doing rather than offering to split the cost. Take one job entirely: the table, the lifts home, the clearing up. It is a smaller offer and usually the more useful one.