Not all horses are able to self trim. Maybe they don't do the miles, maybe their work load is inconsistent, maybe everything they do is on the squish.
It can all end in tears. See the first foot, more or less self trimmed. Then look at the second and third photos. The latter in particular via the wobbly event lines show just how 'out' the foot was.
Went from very lame to high mileage performance horse. Not overnight obviously.