What are you talking about? Funding from state, local and federal transportation sources spent on this does take potential funding from infrastructure improvements. Your statement makes no sense. Not smart.
https://www.railstotrails.org/build-trails/trail-building-toolbox/funding/acquisition-funding/
Keep in mind that not all infrastructure projects make any economic sense but are designed and planned for purely political reason (i.e., to payoff constituents).
BTW, the best way to finance infrastructure is to link it to the economic benefits it creates. No economic benefit, no infrastructure project.
No bridges to nowhere.
BTW, the amount of spending on rails to trails is comparatively minuscule.