I believe he was a local, looked inoffensive and normal and blended in. And after all most of these women had to eat and get a bed for the night. Most didn't have relatives in other district they could stay with for weeks at a time, and how long the murder spree would go on for, nobody knew.
Sugden quotes Dew as being amazed at the hardiness of Whitechapel prostitutes. He remembered after the murders if they ventured out at all 'it was in terror-stricken groups'. Then time would pass and there would be no more murders and the groups would dwindle to pairs and then to sole streetwalkers. Dew recalled the black humour of some of them who would call out as the passed him "I'm the next for Jack!"