Why is Ezreal's dash considered so good

Because is a flash, not a dash. It has decent range (farther than some, shorter than others), he can lower the CD, and because it can't be interrupted except through death.

low cd, goes through walls, comes with a bit of single target burst with decent base damage (275 at max rank)

cait, lucian, and corki cant really use there's offensively as well as ezreals

It's a fairly long range blink that doesn't leave any evidence of the path he took and can have its cooldown reduced by his long range harassment ability.

Lucian, Corki and Caitlyn don't blink, they dash. Most of them have about the same range, although Corki's is a good bit longer, but Ezreal's is a blink. This makes it easier to avoid skill shots and AoEs.

It also deals burst damage to the nearest target within range. It gives him a controlled amount of burst that's worth about as much as a basic attack (unless you've gotten to the point where you have IE and Shiv).

It also has a cooldown reduction mechanic, through Ezreal's Q, on top of a low base CD. 11 seconds, can be 9 seconds if you land two Qs (on ANY enemy), can be cut down to 6.6 seconds (~5 seconds if you land two Qs).

Overall, it's a pretty strong ability. Lucian's doesn't apply any direct damage, Corki's leaves a DoT trail that's easily avoided, and Caitlyn's fires a shot in the opposite direction (which is also pretty easily avoided if you aren't point blank).

Because it's a blink, and a blink with a damage component on top of that.