Dad left mum with 3 young children on a flight

I got a flight today. Sitting nearby was a you mother with a very young baby, a 3 year old and a 4 year old. I guessed the ages but they are around that. The 4 year old was a girl and was crying and screaming as children do on flights. She didn’t want to sit, she didn’t want her seatbelt on, the mum had the baby in her arms and couldn’t do much, the 3 year old was well behaved but couldn’t get the seatbelt on, was frustrated and the mum was so unbelievably stressed. Flight attendants helped as much as they could, but were limited in what they could actually do.
I realised that the father was sitting across the aisle in the middle seat, just chilling and relaxing, waiting for the flight to be over, not a care in the world.
Why couldn’t he take the older 2, so the mum could focus on the baby? Or he could take the baby so the mum could sort out the children? He stood up before the seatbelt sign was turned off and the flight attendant told him to SIT DOWN over the PA. I hoped he would fall. He did not. Asshole.