polyhouses and any other associated with these like vertical farm,hydrophonics etc are firstly suited for specific set of plants.
Not all plants and veggies can be grown , some plants cannot be grown inside polyhouses at all, i would say almost 70 % of veggies which are mass consumed can never be grown in polyhouses,hydrophonics etc.
Just think of all the veggies you had today or yesterday and you will easily understand these cannot be grown in polyhouses let alone hydrophonics.
there is no doubt significant increase in production, compared to outdoor farming. These are because of various factors. The main factors are we allow the plant to grow suitably thereby maximizing required production.
For example in a capsicum polyhouse, there are nets which help the plant to climb, and almost everything is supplied to the plant on more than required basis.
The capsicum plant is allowed minimal leaves so that max nutrition is allowed for the capsicum alone and not for the plant leaves etc. You can think of it it like a kid with a silver spoon, these plants get everything in return for capsisum and capsicum alone. ( who cares abt capsicum leaves BTW )
Secondly The price of capsicum is not determined by the buyer nor the producer , its determined by some trader who is totally unknown. This unknown person gets to decide on the price.
You the end customer nor the farmer has any say in determining the price. This is especially difficult when the output is perishable. The farmer has to sell it at whatever the price which is offered or else his produce will rot. When you grow a bumper crop its all the more difficult to find that many no of traders , transport etc. Selling 1 Ton itself is difficult enough, imagine the complexity when you have 10 tons from the same farm. You would need more resources to manage everything. The trader will never offer the same rate as he would have offered for 1 ton since he knows very well that you would never be able to sell 10 tons.
No country has the ways and means to distribute all the produce effectively across to its citizens.
The problems with polyhouses compound when other methods are introduced ( think hydrophonics,aerophonics,vertical farming etc), There is no economics involved in these.
Unless you do it as a passion. its never profitable to grow brocolli or lettuice in hydrophonics. The trader will never give you the right price if you have an huge quantity.
Its very easy to say brocolli sells for $X and we can do this and that and reduce it by $y in reality no one can control every aspect of the food chain.
Isreal does it becuase of its limited land availabilty , not with the case of India ,china and USA.
I am not sure if I had explained the whole correctly but Hydroponics + etc is only a hobby never commercially viable.