What is diastasis and why can't I do normal ab work with it

Diastasis is a separation of the rectus abdominis muscles that often remains after pregnancy. It's not rare and it's not a sentence.

The trouble is that with diastasis, the usual crunches send the load to the wrong place: the belly can bulge more rather than draw in. So the work goes through breathing and the deep muscles, and the load builds gradually.