Why are newer laptop video cards unchangeable?

what makes them so unchangeable? and I don't mean the integrated video cards.|||1. never knew older graphics cards were changeable



2. they are proprietary stuff and hence not sold in stores



edit:

i would like Dana above to please clarify which dell laptop allows graphics upgrades

also, what is this slot you are referring to|||They are not cards, they are chips that reside on your motherboard.|||Good news is---you can get a upgrade on some laptops. I know I can on mine from dell. I think some will upgrade using the card slot, but most are not changable. Soldered in.

Desktops were made to be interchanged.|||the fact that they are soldered onto the motherboard. laptops have very limited power so they have to be designed around certian power hardware , and graphics cards bary greatly in power consumption , and cards are different sizes so you cant really make interchangeable ones for laptops .