There might be a few reasons for that: 

1) When you complete a delivery, you get paid for it right away.  The delivery happens when the truck with the finished products leaves your sawmill. Each delivery gives you part of money indicated in the order total amount. 

   
By the time the whole order is finished, you’ve already received all the money for it. Once the order is fully completed, you’ll also get the Biz Points. 

2) Sometimes you might not notice a change in your money balance because of rounding. This happens when the amount is less that you have now, and the game rounds it,  so it may not show up immediately on the counter.