Because they were raised in the "it's all about me!" generation. Nothing much matters to them except what they want. That's what you get when you raise your kids to have "self-esteem" without first teaching them about self-respect.
Their wishes trump everybody elses' sensibilities. They can be offended by anything they like, and they expect the world to adjust to their wishes, but if anybody takes offense at something they want to do, that person is condemned as a troglodyte.
You are absolutely correct. The ME generation.
I have a month-old child who is being breastfed by his mother, and I can tell you it is decidedly not all about the mother or what she wants. It is all about the child. Babies do not always get hungry at the most opportune times.
Maybe they have other young children who are swimming and don't want to leave *them* unattended while feeding an infant.