I’ve lived in 4 different flats in the Barbican and they all had a dishwasher. I think only the studios you’d have a problem finding space for one. Of course in the others it is a preference whether you want to lose space for other things or not. It is not a lot of extra plumbing. It is usually when they want to preserve the original kitchen (or a cheap landlord as you suggest - although all the ones I had there were great)