Motorists pay that too.  And gas tax.  And registration fees.

General (no-usage) taxes do pay for part of roads.  We could arguably call that paying for the benefits of roads that we don't individually use, like what they enable for police and fire rescue, for utility maintenance, for construction equipment, for delivery of goods and services and mail and packages, for pedestrian use, etc.  There's a who bunch of usage of roads that isn't someone driving their car, or riding their bike.  General (non-usage) taxes are appropriate for that.

But that only covers part of the cost.  So we try to get the rest from the actual users, because there's a certain fairness to that.  Right now that's mostly from motor vehicles, in the form of gas taxes and registration fees.  But if we have the reasonable ability to also collect a small usage fee from bicycles, that would be appropriate.  And we do have that ability since it can be tied to the vehicle itself.