People living abroad but still using our NHS

Just spent several weeks in Europe on holiday and during that time spoke to quite a few ex pats who have lived abroad for many years , some in their 60’s but quite a few much younger. They all bar one exception fly back and forth to get treated on our NHS . They do it by registering at a family members home and registering with a doctor locally . AIBU to think this is wrong as they don’t pay anything into our health service ? A few of the operations were a new kneecap , heart stents , to have s baby by C section . The country they live in has fantastic health service but they have to travel to the mainland for major illness and don’t want to do that . With the state of our NHS I think this should be stopped