I would venture the following: It's unnecessary to mandate checking Arba Minim.
Why do we need to check our tzitzis?
Casually glancing at your tzitzis will not reveal their Kosher status - there's no visible difference between 6 and 8 strings to the casual observer.
Tzitzis are worn all day - and are mostly out of sight. When they become pasul you wouldn't know about it; the missing string doesn't leave a trail.
If you don't check your tzitzis regularly you'd never notice they were becoming untied and strings are missing.
You don't hold the strings when you make the Bracha or put them and over time you'd forget about them if you didn't inspect them. And when you collect them before Shma you're (1) concentrating on getting ready for Shma and (2) you have no easy way to tell if you're holding 32 or 30 strings.
Arba Minim - when left alone - don't usually become Pasul.
Before you make the bracha you are holding them in your hands after carefully picking them up.
What would make them Pasul?
Most of their leave falling off? You'd notice the pile of leaves when you pick it up/unwrap it. You'd also notice the bare stem.
The tips being cut off? How did that happen without you noticing it? Obviously if you bump your Arba Minim against something you'd glance at them to ensure their integrity.
Black spots on the Esrog? How would that happen once it's been declared Kosher?
The Pitum falling off? The become brittle-dry? I'm sure you'd notice at a glance.
The Esrog shrank past the size of an egg. You'd probably notice that.
So unless you're really distracted you'd notice them becoming Pasul.
Obviously, if you just let a group of tourist shake them, you'd want to glance them over - but what are you going to "inspect"?
