Wetlook World Forum

https://en.wikipedia.org/wiki/Appleby_Horse_Fair

That's a bit bland; I've read a fair bit about it in newspapers and magazines over many years, because of the wetlook pictures frequently displayed next to the articles having caught my attention!    Basically, the great looking ladies are gypsies.   Many would argue that the gypsies (or Romanies) who deal in - and in some cases travel about pulled by - horses, which presumably includes most of these ladies, are a higher class than the usual scrap dealers.    

This is the big social event of their year, where they all get together; though there are no organised events, apparently gypsy weddings frequently occur; in addition, it is no doubt one of the main places where the foundations are laid for next year's weddings, if you get what I mean.    Plus its probably the only time in the year when they are 'in the public eye' in a big way - and a mostly positive way; most of the time in the UK gypsies are regrettably subject to a lot of prejudice ("pikeys" is the usual derogatory name these days).    

So I think the probable reasons they are dressed up are:

1) Best chance of the year to catch the eye of a young man from another gypsy family;

2) Going to a wedding or similar later (or earlier);

3) Want to look their best for the admiring public, photographers, etc;

4) Or simply because they want to look a bit special for the biggest weekend of their year.

As for the photographers - well, its something a bit different, a bit exotic, and part of the ancient traditions of the north of England, I guess.    Most of them do seem to do a lot of the gritty northern stuff in the rest of their output (though I believe a couple may actually be gypsies themselves), either that or lots of country pics.