Why hasn't a withdrawal been made , when I've signed up for a payment plan here on TurboTax? This happens every year.

Ok ... so you know this happens every year when you set up a payment plan so you should know the drill by now.  First, when you are on a payment plan RULE #1 is you do not get behind again or the payment plan you are on can be cancelled and a new plan may not be accepted.   

Next, the IRS can take several weeks to approve your proposed payment plan which means the scheduled payment may not happen right away however make sure the amount is in the account now since the exact date the first payment will happen is unknown.   

Then finally ... you can skip the payment section in the TT program and set up or  check on the payment plan(s) you have online here :  https://www.irs.gov/payments/online-payment-agreement-application