There were a couple of reasons:
Firstly, I'm listening to more podcasts. Indeed, the second part of Russ Roberts' interview with Milton Friedman is the first podcast I ever recall looking forward to.
Secondly, there are now more free newspapers in London than I know what to do with: Metro and City AM in the mornings, "The Wharf" and "The Docklands" once a week near home and "London Lite" and "thelondonpaper" now in every evening.
Thus, the twenty minute periods I used to spend reading the Economist are now spent speed-reading the free-sheets or listening to PodCasts.
The idea of buying a daily newspaper no longer even occurs to me.
Andy comments that he hasn't seen any of the evening papers yet. For what it's worth, London Lite sucks but thelondonpaper is surprisingly good. Given that Associated (publishers of London Lite) need to protect their 50p-a-day Evening Standard whereas News International (publishers of thelondonpaper) are trying to destroy the Standard, perhaps none of this is surprising.
Andy also asked why the free papers (with the exception of Metro) were unavailable inside train stations. The answer (as far as I know) is that Transport for London view the right to distribute papers in their stations as valuable and so auction it. They sold the rights to the morning rush hour to Metro and will shortly be doing the same in the evening. Until they do, nobody has the right to distribute free papers inside their stations - hence all the people outside zone one stations thrusting papers at you.
My advice: take a "thelondonpaper" and politely refuse London Lite.