This couple run the trailer park (which in the UK has no class connotations) on which they live, so I suppose they are used to their shoes being muddy.
Often elderly people are thought of as being unable or unwilling to remove their shoes, but this is not always the case. The gentleman was diabetic. Some medical practitioners (particularly in the USA) give quite rigorous advice to diabetics, encouraging them never to go without shoes. Not all medical practioners take this drastic line and not all diabetics follow it either. Not all people with diabetes develop problems with their feet, though they need to make sure they look after them. The NHS website has a link to Diabetes UK, which gives advice about footcare, but does not insist on the 'wear shoes all the time' rule. It says:
'Fortunately, you do not usually need to do anything very different from other people – general advice on footcare applies to you.'
I thought it interesting that my mother though having a shoes-off rule was 'posh.' Generally people seem to think requiring shoes off is 'tacky.' Nevertheless, when she visited some relatives over the weekend, she took some slippers with her to wear, so I am obviously having an impact.
