The entire concept of the handgun is to have something small and light enough that you can get it into a fight.

Power and [practical] accuracy are secondary to "you always have it on you"- you can always shoot your opponent multiple times if you have to, which is why the dominant handgun caliber (9mm) is one that makes doing that very easy.

The Desert Eagle defeats the entire point of that compromise. It's big and heavy, still makes accuracy compromises [while very mechanically accurate, it's just really hard to shoot a handgun well as opposed to a rifle; that's why rifles have stocks on them], and is still not quite at the power level of a "proper" rifle [simplification: the bullet is not going fast enough].

But that doesn't mean it's useless; in fact, it's quite useful for 3 things.

First, to make a statement that you don't care about practicality/just want Big Gun Energy, which is why carrying one for defense is a meme (that one can fall into with certain degrees of paranoia- when enemy appears, get big, that's how every other animal does it). It's why you see it in movies and games- it's way nicer if you don't have to carry the 10 pounds the gun and ammunition actually weighs. "Because it's cool" falls in this bucket.

Second, for handgun hunting (and to a point big game defense). Despite what I just said about not being quite as powerful as a "proper" rifle, it's still deadly to anything on 4 legs within 100 yards provided you can actually hit it, and the Desert Eagle has some advantages over revolvers in this regard (its trigger is better and doesn't require you to do a separate action to take advantage of it, you can very easily mount a scope on it, and you have more capacity than a revolver offers if that 4-legged thing charges you).

Thirdly, for silhouette shooting (or bowling pin matches), which are the only types of competition that will care if the gun "kills" the steel hard enough at extended ranges. It's actually much better than a revolver here; the added weight makes it more pleasant to shoot.