Why laptops are not upgradable till date ?

In desktops we able to change GPUs. But Why laptops were not made like it ?
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In desktops we can buy a PC without dedicated GPU and add it aftermarket ? Is it possible in desktops ?

That is , If I buy a laptop with integrated GPU , can I able to install a dedicated gpu (say gtx 1050ti ) to it ?

RageshAntony said:
In desktops we able to change GPUs. But Why laptops were not made like it ?
.
In desktops we can buy a PC without dedicated GPU and add it aftermarket ? Is it possible in desktops ?

That is , If I buy a laptop with integrated GPU , can I able to install a dedicated gpu (say gtx 1050ti ) to it ?

It is possible to get a laptop without dedicated GPU like Razer Blade Stealth and use a GPU later through external enclosure like Razer Core.
There are laptops with MXM GPU slot if you don't want to carry that enclosure. Note that not all laptops will have either of these features and those which have either, are pretty expensive.
1050Ti is a solid entry level GPU (for ~60k budget laptops) and there's no point in "adding" it later to the laptop (why stop at 1050ti?)