In addition to some of the things that were already mentioned.
League Operators have to actually put teams together,
Contact team captains,
Find subs,
Figure out table assignments,
Fill out all the registration fees to the national league,
Get everyone sanctioned (include mailing in payments for every player)
Team Shirts for league and/or nationals.
Working with Room Owner,
Printing and Filling out Scoring Sheets,
Making Rules,
Handling all money, including opening bank accounts and managing all expenses, keeping records of what each and every team paid each week (Because people are always short, missing players, subs that don't pay, etc.)
They have to watch shots,
Make Rulings mid match (All while probably trying to play and have fun themselves),
Handle any Banquet, payouts, trophies, plaques, etc.
Manually entering every single game into a computer,
Printing standings both individual and team,
Calculate averages, handicaps, etc.
Come to league early, often leave late 20+ weeks in a row.
Handle stuck balls, jammed tables, 8-ball breaks, etc.
Get to the room early and make sure all the equip is functioning,
Getting players registered for Regional and National Tournaments,
Negotiate room owner to give a team drinks/food,
and more that I'm forgetting.
It's a ton of work and $50/week is nothing for the effort in my opinion!