In my experience in the US, every bike trail/walking trail success has been local; a local group in the area that can benefit from it, getting support from businesses and people in the community and working with the local government.

They sell it as an "option" not as "let's ban all cars" which helps people either support or ignore it, instead of being opposed. Often they work for years, talking to the railroads (lots of these are rail conversions, see https://www.railstotrails.org/policy/ ), etc. They work on plans that slowly take shape (for example, widening sidewalks when they're replaced, modifying roads when replaced, etc). After 10 to 20 years, it all starts coming together.