Question

why are tidal power plants not being developed extensively.

Answer 1

Most everyone has heard of hydroelectric energy or hydropower, that uses a dam to store water in a reservoir.  Water released from the reservoir flows through turbines, spinning them to generate electricity.

Tidal turbines harness marine currents and tidal energy using tidal stream turbines that work much like submerged windmills, but are driven by flowing water rather than by air.MARINE CURRENT TURBINES

But there are other types of hydropower that harness marine currents, tidal energyand wave energy, also referred to as marine current energy. Tidal stream turbines work much like submerged windmills, but are driven by flowing water rather than by air.