Veolia Southwark

We went to the waste treatment plant in southwark and saw very large machines processing the whole of southwark's waste, and although it was a waste treatment plant, it didn't smell very strange. There was also a display at the entrance of some of the things that are made from recycled waste. However, I always had a question about the waste sorting, which was that the waste was not separated into different types of waste, and there were people to sort the waste. And the rubbish trucks also dump all the rubbish together, so what is the use of separating our waste in advance?