Unless you live in one room, everybody has got space for more than one bike. Sensible people don't save their hard earned cash to buy high-value items to leave unattended on the street in high-risk areas. They buy the cheapest thing that will do the job which carries the smallest financial loss if it gets nicked. You don't buy an expensive bling watch to tell you the time working on an industrial site either - you make do with a £10 one from Argos so if you smash it or lose it, you aren't going to cry about it. There's loads of cheapo commuting-suitable bikes on the secondhand market. I bought an Apollo CX10 for £1 a few months ago purely to strip for parts. It was in very good condition apart from worn tyres and if it had been big enough to fit me, I would have been quite happy to use it as an on-street hack bike.
Some people will steal anything, but most thieves want items with some value, which means they aren't going to bother taking your £20 hack if someone has left a tidy-looking £500 bike parked next to it. I'd rather have to replace a £20 bike than a £500 one, but if having a shiny bike to ride to work on in the morning is more important to some people than still having a bike of some sorts to ride home on gain in the evening, that's their lookout.
