Lots of these anomalous styles about, they exist where there was once a field margin to cross. Hedges die out, post and wire replace them, then they get knocked down. The loss of our small dairy herds have meant that many larger areas of purely arable cultivation, without the need for stock proof fields boundaries. This has increased the hidden loss of hedgerows, which I am afraid is aided by the RSPB's attitude to hedge management. Well maintained thorn hedges are cheap stock proof field margins, but for a period of their life they need to be cut in the spring, banned by RSPB, weed species and overgrown thorn hedge plants soon get knocked out by cattle, leaving an isolated stile in the stealthily enlarged field.
Course the other cause is blind bureaucracy feeding an unquestioning factor, 'who' today, with targets to meet, will question a docket that says put up a stile where it is not needed. A fence line is on a map somewhere in town hall, overweight buttocks in swivel chair clicks a print command. One more sturdy decision towards early retirement.