As far as Moondance's argument about road racing not belonging at the Olympics as it's not the most prestigious event in the sport, there's something to that.
However, I reckon road cycling deserves a bit of latitude, even though it's clearly less prestigious than winning a Grand Tour (or, for that matter, probably the Worlds or some of the classics).
For most of the population of a host city, it's difficult to actually get to see many of the decent events. Sure, you can get cheap tickets to see Zimbabwe play Colombia in the field hockey, or sit a mile back in the main stadium for the heats of the 400 metre hurdles and the shotput finals, but the good tickets to the good events cost a fortune and/or are reserved for whomever Coke, Visa, and the IOC prefer to shower good fortune on.
By contrast (and except for Beijing) everybody can come out to see the cycling for free.
On that basis, I reckon it's worth retaining as a reward for the citizens of the bid city who can actually get to see something for the billions of dollars worth of debt they'll be paying off for the decades afterwards...