Private venture bike shares are typically funded by an advertising management contract (such as to sell ads on city buses, bus benches, etc.). If the ad revenue isn't enough, the private company won't do it, hence the variety of programs being funded by public sources.

Like Portland, the City of New Orleans would love to have a bike share program; however, New Orleans is broke and no other entity has stepped up to fund it.

RideTHISbike
New Orleans