The difference is that there is not an equivalent instruction in the Highway Code (or elsewhere) suggesting that pedestrians should wear helmets, nor is it common practice for pedestrians to do so.
It's not an instruction, it's a recommendation. The only time, by law, that you have to obey the highway code is when it says 'must'
It's not an instruction, it's a recommendation. The only time, by law, that you have to obey the highway code is when it says 'must'