The real answer is, of course, 'because nearly 20 years after their publication you will want them for period detail for a novel partly set in late 1980s London and they will provide an excellent source of information as to what the characters will get up to, the costs of things (meals, accommodation), gigs they would have gone to, etc. etc.'.
The need for this information is amplified by the fact that I have arguably never lived in London (depending on your definition of London) - certainly not in student accommodation, though I did visit students in London in that era, though only one in a proper student shared house of the sort we know and love, the others were 'digs' in the living with landladys sense or in halls of residence.
Also, for plot reasons, the characters are a few years younger than me so I need to work out how much poorer they would be due to the erosion of grants, benefits etc.
It is all surprisingly difficult. Maybe I need to find someone who went to London University as an undergraduate in the late 80s and interrogate them in the manner of an anthropologist. 'So, tell me, what sort of travel pass would you have bought? Did you buy Time Out or City Limits or what?'
Or maybe I need to write something less ambitious.