Roads are usually paid for with a gasoline tax. This worked out great when everyone drove cars as the more you drove the more you paid. The problem is as we move to alternative fuels there will be no one left to pay for the roads.
Bike lanes cost money to build, and money to maintain. They may not get worn out by the bicyclists but they still need to have the street sweeper run, the lines painted, signs posted, cracks sealed, etc. Around here the bike lanes are not used nearly as much as the rest of the street, I would say probably the bike lanes cost more per mile used than the rest of the street.