I would think that prior to the Mears contracts, the valets were Disney employees, and their wages and benefits were shared as part of the common areas for the combined
DVC-Cash resorts. Remember that the free standing DVCs (OKW & SSR) have never had valet services.
As minimum wage increased, along with associated employee costs, like health insurance, retirement, etc., Disney decided it was more cost efficient, like many businesses, to contract out he valet services and remove those employees from the Disney payroll system. Likely the first year or so, the previous Disney employees continued to receive some Disney benefits whose costs were shared by the DVC-Cash resorts. Probably with this latest cotract, the benefits have shifted completely to Mears' responsibility.
I do think DVC tries to fund the most used items for members. I would guess that the "free" internet, while quite a bit less to fund than valet employees, is also used by a higher percentage of members than the valet service. Look at all the threads we had over the year prior to receiving the internet from members complaining that even Motel 6 and Super 8 have free internet, plus laptops and other portable devices (ones where you may need to supply your own wifi router) have become much more common place for travelers.