Tens of millions of people are working in small offices or interacting all day with the public. Hour upon hour spent next to infectious people, and whilst masks might lower transmission somewhat, they're not enough to stop you getting infected in these places.
On my 90 minute dog walk today I saw one person from a long distance (I drove a few miles to somewhere quiet).
Why focus on the trivial when the main problems are indoor mixing at work and schools? Who cares if Boris goes on a bike ride, or someone drives 10 miles to exercise - it makes essentially no difference if done sensibly.