My take would be:
Why in urban areas?
Well over 50% of the population of the UK lives in urban areas now. I was a warden for a remote nature reserve for some years. We would host various groups staying overnight in our hostel - some there for wildlife watching or similar and some because it was close to a nearby arts festival. A lot of the arts groups were mainly urban in background and I could very clearly see the difference. So many people in these groups simply didn't understand what they were looking at around the reserve and didn't place any value on it. I recall one jazz trumpeter who had never spent much time outside of London. 48 hours in to his stay he was climbing the walls. You could hear birds singing. According to him "It's not natural!".
Politicians make policies and allocate funding in light of what their constituents value. If people don't value wildlife the little funding that we currently have is just going to be cut and cut.
Why less affuent areas?
If you are living in a less affluent area, chances are there will be fewer greenspaces around you - and there is plenty of research that shows that access to greenspace improves heath and welbeing in a whole range of ways. Chances are that those greenspaces won't be as well looked after. And chances are that you are going to have less money and less time to spend on transport to take you further afield: to spend time in the countryside or nature reserves where you can connect to wildlife.