No one can possibly watch their child for every second. Let alone more than one child. So there may be parents who are highly engaged and curious and just deeply deeply unlucky.
That said, I do think many people including parents do not give enough thought to water safety.
Most children who drown are within 20ft of an adult. It's not toddlers sneaking off on their own that is the highest risk but the kids in the pool with adults or with adults just nearby.
Drowning is silent. There is no screaming and waving. Films are very misleading about it.
Children will look like they are climbing a ladder as they drown as they will be vertical and frantically using arms and legs to try and climb (which is why you need to try and teach them "float to live").
Their mouth will bob just under the water, they inhale some but manage to get themselves up through their frantic ladder climbing, it happens again and then again and then they've inhaled too much and drown.
It can look a lot like they are just doggy paddling. But always look - is there mouth going under? Have they gone vertical, rather than horizontal?
If so, grab them immediately.
No screaming. You can't scream if you are actually drowning.
I grabbed a boy at a busy beach who frantically ladder climbing, just as the lifeguard also noticed and leapt in to get to him - the lifeguard then told me off for not keeping a close eye on him (once he was safely out of the water!) and I explained I didn't know him. His dad had not only missed his son drowning but missed the lifeguard running and diving in, his son being taken out and wrapped in blankets and checked on the beach...
But he was lucky and the boy was fine, if a bit shocked.
He had another child and thought the boy was a much better swimmer than he was.
Much better parents might still be much unluckier.
Reducing the probability of it happening is important of course but using any individual case to cast aspersions on that family when we have no idea what happened is not fair.