Why are graphic displays still so expensive?
It's also to do with supply chain. 

A component you buy on digikey or RS etc has a very significant price overhead attached to it. You are paying for the convenience of the supplier (digikey or RS) cataloguing items, packing, shipping, 

A finished LCD monitor as product can benefit from all the advantages of volume production and the efficiency that comes with it. 

When it comes to displays versus integrated circuits, there is another difference: Displays are usually made custom to-order. It was somewhat different when it came to 2-row alphanumeric displays, but things like OLED displays are not standardized. When I design a product with a display that will be manufactured in the hundreds of thousands (or even less), I will talk to a display manufacturer directly, and have them built to-order my design. The displays sold by distributors are so expensive because another intermediate company actually designs, orders, and assembles the display as a module, and then sells it to the distributors you buy from. They are targeted at prototyping/low volume, where that cost is insignificant in the scheme of a product-development cycle. This can also be seen in the price. 

It is somewhat similar to integrated DC/DC bricks. You can make DC/DC assemblies with the same performance for a fraction of the BOM and assembly cost, but the design cost, and the benefits of having that product now, outweigh the higher cost of a pre-made module.