Depends where they are .... Commercial rents, insurance, wages, have all gone up. Add to that cross-hire, L2 costs, aircraft maintenance (parts), landing fees, owners / Club / shareholders wanting/needing more dollars for profit, expansion etc.
The first ultralight club I was involved with had a volunteer instructor & L2, borrow or BYO plane. Then they got a loan to buy a plane, the instructor wanted paying (only a pittance), the L2 asked too, but settled for an hour free flying for every half hour spent maintaining. Fees went up accordingly. Then they both wanted more, interest rates went up, the Club needed a hangar for the fabric aircraft, more fund raising ... Needed more students, advertised and started getting people from away, L2 & instructor said "we want commercial rates now". Then the drought took a grip, students dried up too, funds accumulated for the new hangar went on site rent, repayments etc until it was all gone and the plane sold. This was 15 years ago. Nothing new. If the market won't bear it, the operation folds. If they don't charge enough to cover day to day plus future & unforeseen (replacement, upgrade, prangs etc) they go bust. Holding off on fee increases gives the impression of a cash grab, gradual small increases seem to be the better strategy.