I think a lot of agencies wont get loads of decent girls like they used to years ago, so easy for the girls to set up on AW don't cost anything, instant work, charge what you want, choose who you want to see and no paying agency.
If I were a WG I wouldn't be wanting to agree to give a pimp 30-50% of my fees. Clearly it suits some WGs though who cant afford their own premises to work out of or cant work from home, and some others as all they have to do is turn-up and punters are laid on.
One point though A/W isn't free to WGs, any credits accrued are subject to a 30% take from A/W, though I assume you mean its free to put their profiles on A/W.
In London its even worse value with many Agencies as they don't provide the WGs premises so they have to provide them and still pay the same kind of cut to their pimp that a WG who works out of a Parlour does. Pimps who don't provide the premises which is the legally smart thing to do as they cant get done for running and brothel in addition to controlling prostitutes for gain are getting money for old rope in my view. Up to WGs of course how they decide to work.