The boys have become complacent, and take their lack of cleanliness as normal.
At the beginning of the chapter, Ralph wonders about this. He even wishes for scissors to cut his hair, a bath, and a toothbrush. When Ralph looks at the dirty boys, he realizes he finds himself thinking that none of them is “an obvious subject for a shower.” This disturbs him.
He discovered with a little fall of the heart that these were the conditions he took as normal now and that he did not mind. (ch 7)
The children have been away from civilization for so long, that they no longer even wish for it. They make few attempts to keep clean, and worry about baser needs like food. At the same time, they seem to enjoy their rough lifestyle, with no one telling them what to do.
Golding is making a stark commentary about society here. He is essentially saying that we have standards for only as long as someone is enforcing those standards. Since there is no one on the island to tell the boys it is a priority to be clean, they don’t bother. Also, on a deeper level, it is not possible to take care of higher needs until lower ones are met. If you need food, you are not worried about a toothbrush.
As a society, we are only able to keep neat and clean because all of our other needs are taken care of for us. The boys are incapable of doing this.