Two things are happening here..

1. The casino does not have the available cashflow to payout large withdrawals, so they pay in smaller increments as new money come in.

2. They draw out the payment process, knowing that the gambler will continue playing and will also lose most of his/her balance ..so eventually it will be much less to payout.

You have to hand it to these small casinos, they have genius backup plans to manage a small bankroll..... and they also know how to hide it.