Is it just a matter of not being worth it? I see cooling towers releasing what appears to be a ton of steam, pretty high up. If that steam were captured at the top and allowed to condense, wouldn’t that result in a ton of water with a lot of gravitational potential energy? That water could then be released and used to power water turbines. Maybe I’m overestimating the amount of water being released as steam, or underestimating how much is needed to spin a water turbine to get a meaningful result, but it seems like wasted energy to me.
Because efficiency. The amount of power generated from the water fall would be minuscule compared to the power generated from the stream.
Any engineering effort going into making this process more efficient would be better off making the steam generation more effective.
Short answer is because it isn’t worth the effort.