Why don't they?
Kids, unsaleable (historic) houses, jobs, horses, and pensions in the UK. One of my friends, a lady of 60, can't seem to find a job here that would replace the small business she runs in the UK that appeals to a niche market which doesn't exist here. Another has a disabled grandchild and her help is needed to care for him. Etc. Sometimes it's not easy to pack up everything, leave the people you love and won't be able to see much anymore, and get reestablished in a new country.