I'll make a comparison.
If you buy your own home, you're responsible for the maintenance, repair, roof replacement, landscaping, utilities, etc.
Similarly, if you buy a condominium, the condo association pays for all of the expenses you would normally have paid for a single-family home, except that you'll pay for some of the utilities yourself. The condo association charges each owner a fee to provide funds to pay those expenses.
If you (and perhaps some other owners) stop paying your condo fees, the condo association will not have enough money to cover expenses and the property will soon be in a shambles. Thus, condo associations are formed in a manner such that acquiring ownership in a condo legally obligates the owner to make the required fees. Doing otherwise would make the financial arrangements for condos completely unworkable and condos would not exist.
A timeshare resort is set up exactly like a condo association. The primary difference is that instead of one owner for each condo unit, there are usually 50 or 51 owners for each condo unit.
Thus, in order to make a timeshare resort financially viable for both you and me, we are each legally obligated to pay our maintenance fees on units we own.