WYP are one of the worst police forces in the country. They are on a par with the Met. Why this came to be, it's difficult to say. Some people says it is the pool of candidates they recruit from, but there's definitely something seriously wrong with the culture.
What is interesting is that South Yorkshire Police are now very different, yet both regions are similar in that they are post-industrial Northern regions. One reason given to me about why SYP are so much better was that the whole "People's Republic of South Yorkshire" concept sunk into the bones of the young people who are now local police officers so they have a far more communitarian approach, and the outrage and consequences of policing the miners' strikes in the 80s (Orgreave etc) has meant there is a legacy of shame that acts as a bulwark to prevent undue force or unreasonable approaches being employed.
Another reason I've been given is Teresa May. Apparently, so I am told, she "loathed the Police" and cut numbers significantly (I've not checked this assertion). What happens when you cut police numbers is you tend to rid a force of experienced officers that hold the internal culture in place. What happens then, when you inevitably realise you need more officers, is that you subsequently recruit into quite a weak institution where new incomers with very different ideas can shift a culture dramatically purely by force of numbers. If you then recruit the wrong people, you've a serious issue on your hands.
But I think we've got to the point where there needs to be some kind of investigation of both the Met and WYP because they are quite obviously corrupted institutions.