Every reason in the world... the specs are different. That is like putting a chevy engine in a ford.
Laptops are built for the seller by a number of manufacturers... sony doesn't make its own.
The LCD inverter behind the screen on those two models are significantly different... in size and shape.
There is no reason I can think of, knowing both models, why you would think they would fit each other, because the other specifications for processor, motherboard, etc. are not the same.
It is extremly rare that yu can do this with any product from any manaufacturer.

thanks! I see what you mean as I had changed everything out and nothing worked, well I guess I'll go ahead and buy another screen that fits thie model. >

Is your screen broken, cracked, or damaged? Or did it just stop working?
Most Sony VAIO laptops have an extremely high failure rate of the LCD where the inverter has failed. That failed inverter can be replaced for about $75 by a good repair shop or $155 by Sony. If you replace the screen, be sure to also replace the inverter.
As with the other stuff, the inverters are usually NOT interchangeable.