Not all the presenters live in London. Some live in the outer reaches of London or in the Home Counties. Some of them commute from further afield (Jackie Kabler lives in Gloucestershire, Marv is based in Birmingham and comes down and stays overnight somewhere when she's got back-to-back days with awkward hours. Same with guest presenters and models, not all of whom are even based in the UK.
I imagine most people in the entertainment field have multiple jobs to keep the income coming in. Those presenters who have websites - you can see they are basically all guns for hire. They will have a contract with QVC (but who knows, it may be a zero hours one for all we know), and they will have other media work, plus their other interests. Micael and Craig are the only two men that appear to be London-based, and Chloe is or was in London - I remember during her first year, she ended up coming in to cover sickness and snow-days at very short notice.
For the others - it could be that for both male and female, their partners are the main earners.